问题 选择题

能对污水起净化作用的单细胞生物是

A.酵母菌

B.草履虫

C.鼠妇

D.蚯蚓

答案

答案:B

草履虫是一种低等原生动物,能把水里的细菌和有机碎屑作为食物摆进口沟,再进入草履虫体内,供其慢慢消化吸收。据估计,一只草履虫每小时大约能形成60个食物泡,每个食物泡中大约含有30个细菌,因此,一只草履虫每天大约能吞食43200个细菌,它对污水有一定的净化作用。

多项选择题
单项选择题

礁糊秀

The most romantic time to arrive in Venice is at dusk on a winter’s day. Your water-taxi ride across the lagoon from the airport will catch the last velvety-grey streaks of daylight. You’ll arrive on the Grand Canal just as the upper windows of its palaces start to bloom with rose-coloured lamps or sparkle with chandeliers. In no other city does evening begin with such promise.

Strange, then, that Venice should be so emphatically not a night-time place. However mobbed it may have been in daylight, darkness falls with the abruptness of a hauled-down shutter. The crowds of Asian tourists and schoolkits milling around seem to vaporize. In a hundred closed cafes, the espresso machines give an expiring hiss, as if at last slipping off their shoes and wiggling their toes.

That is what makes Venice by night so magical, when the loudest sounds are those of footsteps and lapping water, and the modern world recedes so that in any Square or over any bridge, you wouldn’t be surprised to meet a hurrying figure in a cloak and buckled shoes; Casanova on his way to some assignation, perhaps.

St. Mark’s becomes an enchanted place, with pools of the day’s flood still underfoot and mist wreathing the cathedral. But "nightlife" seems nonexistent outside the weeks of carnival each February. In a city so stuffed with historical treasures, the lack of a living, modern culture is achingly apparent, especially after dark.

Venice’s only theatre of note, the Fenice, has only just reopened after almost a decade, following a fire. Clubs, discos, even cinemas are almost as hard to find as car parks. Nor is there the eating-out culture that governs the rest of Italy.

Venice is not usually regarded as a gourmet paradise. Even J G Links, author of the definitive, eccentric guidebook Venice for Pleasure, suggests it has few restaurants worth visiting outside the Cipriani hotel. As a rule, it’s best to avoid canalside establishments with their menus turisticos; look for places down alleys. Remember, this is rice, not pasta country, offering some of the best risotto you’re ever likely to eat.

When I first came here, aged 15, on a school trip, we were quartered in a girl’s convent school. Ever since, I’ve stayed at the Gritti Palace, on the Grand Canal, overlooking the Salute. Apart from its mixture of elegance and old-fashioned comfort, I have two reasons for loving this hotel. Alighting at its private landing stage completes the thrill of arriving in Venice by night. And it was here, 13 years ago, that Sue and I decided to get married and have our daughter.

Gondolas operate until well after dark. It can be doubly romantic, with the Grand Canal in pitch-darkness and silent but for the churn of water buses and scraps of operatic arias that some gondoliers still perform.

Latterly, Venice has been making more efforts to get a nightlife. There is a disco named Casanova near the railway station and a music bar, Piccolo Mondo, near the Accademia bridge. The city’s student population has created funkier areas around Campo Santa Margarita and in Cannaregio, the immigrant quarter to the north.

There is also street music after all the smart shops have closed and the only merchandise on offer is fake designer handbags, set out on the trestles used as walkways at times of flooD.Around one corner, you may come upon a countertenor in an anourak, singing Handel; around another, two men will be playing selections from Andrew Lloyd Webber on a vibraphone of water-filled glasses. You think that sounds totally naff I can tell you it sounded totally wonderful. Such is the alchemy of Venice by night.

Which of the following can best summarize the passage()

A.Venice provides visitors with delicious food of Italian style.

B.Songs and music are special features of Venice by night.

C.If you want to enjoy nightlife, Venice is a wonderful place.

D.Venice is not a good place for nightlife at present, yet the evening of Venice has its own glamour.