We cannot figure out ________ quite a number of insects, birds, and animals are dying out.
| A．that | B．as | C．why | D．When |
To show our respect, we usually take our gloves off _______ we are to shake hands with.
| A．whoever | B．whenever | C．whichever | D．wherever |
To understand the complex situation completely requires more thought than ________ so far.
| A．gave | B．has given | C．has been given | D．is being given |
According to some theories ________ from psychoanalysis, life is supposedly easier; and more pleasant when anxiety is overcome.
| A．obtain | B．obtaining | C．to obtain | D．obtained |
All the ladies wear beautiful clothes for the celebration. Some are dressed in red, _______ in purple.
| A．other | B．another | C．others | D．the other |
Keeping a foreign pet is dangerous, as the owner might be infected ________ the diseases brought along with the animal.
| A．in | B．with | C．by | D．for |