It was when we were returning home _____ I realized what a good feeling it was to have helped someone in trouble.
| A．which | B．that | C．where | D．how |
I am concerned __________ it that I can't concentrate __________ my work because of headache.
| A．of; on | B．of; of |
| C．about; on | D．about; to |
His daughter couldn't concentrate __________ her studies with all that noise going on.
| A．to | B．with |
| C．on | D．towards |
Mr. Bill Clinton was elected __________ President of the United States in __________ 1990s.
| A．the; the | B．a; the |
| C．/; the | D．the; / |
At __________ present we are going through a hard time, but I'm sure __________ things will get better in the near future.
| A．the; the | B．the; / |
| C．/; the | D．/；/ |
The cakes are delicious. He would like to have __________ third one because __________ second one is rather too small.
| A．a; a | B．the; the |
| C．a; the | D．the; a |