______the doors were closed and that all the lights were off, the boy left the classroom.
| A．Check | B．To check | C．Checked | D．Having checked |
It is high time that we ____ the amount of carbon dioxide in our daily life.
A. reduce B reduced C will reduce D reduces
It rained that day and ___ the baseball game was called off.
| A．however | B．still | C．so | D．consequently |
It is not until the disease has progressed to AIDS ____a person begins to look sick.
| A．who | B．that | C．where | D．before |
It is not clear ____the effects of global warming will be.
| A．how | B．which | C．that | D．what |
All the scientific evidence ______ that increasing use of carbon dioxide ______ the rise of the earth’s temperature.
| A．show; result in | B．shows; result from |
| C．shows; results in | D．shows; results from |