If ____ in, viruses can result in illness or even death.
| A．breathe | B．breathing |
| C．breathed | D．to breathe |
It sounds like something is wrong with the car’s engine. _____ , we’d better take it to the garage immediately.
| A．Otherwise | B．If not |
| C．But for that | D．If so |
Only after they had discussed the matter for several hours ______ a decision.
| A．they reached | B．did they reach |
| C．they reach | D．do they reach |
The earliest English ___ was written in a kind of English that is now difficult ___.
| A．poem; to understand | B．poet; to be understood |
| C．poetry; to be understand | D．poetry; to understand |
At the foot of the mountains ____ a tower built in the Ming dynasty.
| A．Stood | B．stands | C．standing | D．stand |
--- Tomorrow we’ll go hiking in the mountain to experience nature.
---- ___ it rains heavily when we are still halfway?
| A．How so | B．what though | C．what for | D．What if |