单选题 We can conclude from this passage that ______.

A、 the heat created in microwave ovens is very difficult to control
B、 food tastes better when cooked in a microwave oven
C、 food cooked in microwave ovens is probably more nutritious than food cooked in more conventional ways
D、 most research on the effects of microwaves on human beings has been restricted to the study of low level microwave radiation

【正确答案】 D

【答案解析】选项A和B在文中并未涉及；文章第二段最后一句指出"Food that have more water．．in a microwave oven”，即对于在微波炉中烹饪的食物，所含水分越多，熟的越快，并且越有营养，而不是选项C所说的与传统的方法相比，在microwave ovens中烹饪的食物更有营养；至于选项D，文章第四段指出"scientists are more concerned about．．．a leaking microwave oven．”，即科学家们更加关心low level microwave radiation对人体的影响，故选项D正确。