Don’t turn off the computer before closing all the programs, _____ you’ll have problems.
| A．but | B．and | C．so | D．or |
When you read the book, you’d better make a mark ______ you have questions.
| A．at which | B．at where | C．the place where | D．where |
I didn’t see your sister at the cinema. If she ______, she would have met my brother.
| A．has come | B．did come | C．came | D．had come |
____ all behavior is learned behavior is a basic assumption of social scientists.
| A．Nearly | B．That nearly | C．It is nearly | D．When nearly |
By the middle of the 21st century , the vast majority of the world’s population ________ in cities rather than in the country.
| A．are living | B．will be living |
| C．have lived | D．will have lived |
It is because people are likely to stay indoors ______ the virus can spread easily ______ people often catch colds.
| A．and, that | B．so, that | C．therefore, so | D．that, that |