. The temperature can fall to –50°._____ is, 50°below freezing point.
| A．Which | B．It | C．This | D．That |
20. The flu is believed________by viruses.
| A．causing | B．being caused | C．to be caused | D．to cause |
19. They________a lot of suggestions for improving the workers’ living conditions.
| A．put out | B．put forward | C．put on | D．put in |
18. After having gone____-far, I didn’t want to turn back.
| A．enough | B．thus | C．that | D．Much |
17. One of the mottos for the park makes_____clear that science and business can and must work together to build the future.
| A．them | B．it | C．us | D．This |
16. This experiment turned out to be____failure, but, as we know, success often comes after___failure.
| A．a; \ | B．a; a | C．\; \ | D．\; a |