题目内容
It’s a serious problem．We can’t decide________ Mr. Harris comes back．
A．while B．since C．until D．so
C not…until…“直到…才…”。故选C。
练习册系列答案
相关题目
| 完形填空。 | ||||
| The most well-known effect of weather 1 mood is a medical condition called Seasonal Affective Disorder (SAD for short).People who 2 from SAD get very 3 and depressed during the winter months. Actually it is 4 to do with the weather-more because during the winter, days are very 5 and people don't see so much day light(especially if they spend most of the day in a school room or of fice!). Of course, the further North of the equator you live, the 6 _ the days during winter and the more 7 you are to have symptom of SAD. When you are 8 to sunlight, your body makes lots of Vitamin D3, and because of that you make more of a substance called Serotonin ( pronounced Ser- ah - TONE- in).Serotonin is a chemical 9 in the brain and it's very 10 to your mood. We know that if you don't have enough of it then you can become depressed-antidepressant drugs like Prozac work because they 11 the amount of serotonin 12 to the brain. Scientists think that some people aren't so 13 _ at making their own serotonin, and need more sunlight than other people to do it properly. These are the people who suffer from SAD during the winter, 14 they just can't get enough sunlight ouring the short days to make all the serotonin they need to 15 happy. This is probably down to their genes. | ||||
|