Until the start of the Industrial Revolution, mankind was poor, hungry, and constantly at the _______ of disease and natural disasters．
| A．power | B．limit | C．control | D．mercy |
Get involved in sports or other activities you enjoy______you can meet people who like what you like.
| A．what | B．when | C．that | D．where |
Why did you take a taxi____you could come here by bus?
| A．while | B．unless | C．when | D．until |
Circus tigers, although they have been tamed, can _____ attack their trainer.
| A．unexpectedly | B．deliberately | C．reluctantly | D．subsequently |
The patients believe that the doctor knows exactly how to put them _____.
| A．correct | B．perfect | C．right | D．well |
They decided to leave the waiter a big _____ because the food and service had been excellent.
| A．note | B．reward | C．tip | D．gift |