Compare the bold part of each sentence with the expressions (a), (b), and (c) given below. Choose the expression which is an improvement upon the bold part. If none of the three expressions improves the sentence, then your answer is (d).

Kindly let us know the time of your arrival by return of post.

I elected him President of the society.

The children are playing in the garden since ten $\mathrm{O}$'clock this morning.

We had better send for a policeman.

There is plenty of time to catch the train.

Hundreds of people were killed by the earth quake.

He insisted on he was innocent.

John, who studies medicine at present, hopes to go abroad after graduation.

The forest is infested of snakes.