问题
单项选择题
进行水力模型试验时，要实现有压管流的动力相似，应选用的相似准则是( )。
A．(A) 雷诺准则
B．(B) 弗劳德准则
C．(C) 欧拉准则
D．(D) 韦伯准则
答案
参考答案：A
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进行水力模型试验时，要实现有压管流的动力相似，应选用的相似准则是( )。
A．(A) 雷诺准则
B．(B) 弗劳德准则
C．(C) 欧拉准则
D．(D) 韦伯准则
参考答案：A
Passage One
| Go Ahead—Cook with It 别怕—就用它来烹饪 It’s grapefruit season. From now through March, the golden orbs are ripe for the picking. And they’re not just for breakfast any more. Hanging around on trees all about California: grapefruit—heavy with juice, tartly sweet, beguilingly perfumed．Round and yellow as happy faces or suns, they seem to ripe just as the general populace sinks into its annual round of post-holiday dietary self-chastisement. Coincidence Perhaps. But we say run with it. Look beyond the obvious salvo of half a grapefruit for breakfast attacked with a jagged spoon and you’ll find a marvelous fruit for peeling and eating out of hanD．There’s nothing like it for inducing simultaneous feelings of gastronomic piety and delight at recapturing a long-lost pleasure. It’s sensual: the aroma of essential oils as they spurt daintily from the pores of the thick skin, the ripping sound of the tenacious segments being pulled apart, the juice dripping down. And it’s delicious. But don’t stop there. Cook with grapefruit. Use its juice to flavor sauces. Section and scatter it. Bake with it. Candy its peel. Grapefruit is milder and sweeter than lemon, but it can be used in many of the same ways—squeezed on grilled fish, made into a brightly flavored curD．And if you’re looking for gorgeous color, red grapefruit offers extra plate appeal. The notion that red grapefruit is sweeter than white or yellow grapefruit is, however, a myth, according to citrus specialists. (The story grew out of a marketing campaign by Texas growers. ) Red grapefruits get their color from lycopene, which has health benefits (its an antioxidant)but does not affect flavor. Sweetness is determined, rather, by the length of time the fruit has been hanging on a tree. A grapefruit picked in December isn’t as sweet as one picked in February, so if you have a tree, just pick fruit as needed． If not, ask at your farmers market about the different varieties available, all of which have their fans. California reds include the medium-pink Rio Reds from the Caochella Valley and the Star Ruby from Central Valley (and Texas). Yellow Marsh is a familiar yellow variety and the Duncan, while not usually labeled as such in supermarkets, is a reliable white. For those who don’t like the tartness of a true grapefruit, Oro Blanco—the half-grapefruit, half-acidless pummelo—is sweeter and can be used in salads. Our salad of jicama strips, thinly sliced snow peas, fresh pea sprouts (available in Asian markets)and red grapefruit sections has an appealing crunch. Its delicately harmonious flavors are pulled together with a faintly sweet dressing of grapefruit juice, tarragon and mint. The strikingly pink sauce of our baked halibut dish contrasts with the white flesh of the fish for an artful plate—and it’s easy to make. Before baking, marinate the halibut in grapefruit juice with garlic and thyme. Sauce it with a reduction of grapefruit juice combined with blood orange juice, which deepens the color and softens the flavor. Then whisk in bits of cold butter for silkiness. A rich crust is a perfect foil for the tangy grapefruit curd filling in our pretty tartlets. Both grapefruit juice and lemon juice are used in the curd to focus the flavor; grapefruits zest enlivens the crust. Garnish them with whipped cream and candied grapefruit peel. For cooking, select heavy fruit, which indicates juiciness. (If you’re making a batch of candied peel, however, lighter fruit will indicate more peel.) Before juicing, roll a grapefruit under your hand on the countertop to help extract the most juice. Avoid lumpy fruit, which may be over-ripe. And finally, for those whose resolute January superegos care about such things, here’s a reassuring thought: Grapefruit is low in calories (40 to 60 each), high in vitamins C and A, and an excellent source of fiber. It contains no fat, sodium or cholesterol. So peel away. |
The sweetness of the grapefruit is determined by______.
A．lycopene
B．the length of time the fruit is exposed to the sun
C．the length of time the fruit is hanging on a tree
D．the specific nutrient the fruit takes from the soil