1)You program the clock with the latest time at which you want to be wakened,and it (?)duly wakes you during the last light sleep pahse before that.
A)THEN B)almost
2)The concept was invented by a group of students at Brown University in Rhode Island (?)a friend complained of waking up tired and performing poorly on the test."As sleep-desprived people ourselves ,we strates thinking of(?)to do about it ."says Eric Shashoua.
A)AFTER B)since
A)WHAT B)how
大写字母是正确答案，我想问的是，为什么另一个答案不可以。说明白的再加分，免得浪费我的分数。