根据灌溉水量与效益、费用关系曲线，在非充分灌溉用水量范围内，_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题判断题

根据灌溉水量与效益、费用关系曲线，在非充分灌溉用水量范围内，虽然所获得的作物产量不是最高，但其净效益却大于最高产量时所获得的净效益。

答案

参考答案：对

单项选择题 A型题

不含有核酸的病原体是（）

A.virus

B.prion

C.fungus

D.bacteria

E.chlamydia

完形填空

阅读下面短文，掌握其大意，然后从1～15各题所给的A、B、C和D项中，选出最佳选项，并在答题卡上将该项涂黑。
Some passengers won’t turn off their mobile phones or iPads during takeoff or landing. It happens on almost every         now. It’s time to turn off personal electronic devices when the plane’s door        . However, there’s always at least one person who keeps talking, texting, playing, watching or emailing — and         strict orders to power down during flights.
“People have become so         to those devices, and a lot of people         whether they really need to turn them off,” says an airhostess from Southwest Airlines.
Is turning off the devices really         in the first place? Lots of passengers have doubted about the         of leaving devices on. They think one cell or message or game isn’t going to         down the plane.
Indeed, there’s no         scientific evidence that having devices powered on during takeoff and landing would cause a        , only that there is the potential of a problem.
In the US, pilots are allowed to use certain electronic devices during takeoff and landing, but if passengers’       devices are tested at the same time, it may lead to wrong warnings and         readings on the aircraft instruments. In some studies researchers found mobile phones could         global-positioning satellite systems or other aircraft systems. Though the effects are         slight, they could result in disaster.
If even the         possibility of disaster exists, it’s better to turn them off during takeoff and landing.