Air pollution caused by industrial fumes (1)has been studied for years. (2)but only recently (3)has the harmful effects of noise pollution (4)become known.

Air pollution caused by industrial fumes (1)has been studied for years. (2)but only recently (3)has the harmful effects of noise pollution (4)become known.

A 1

B 2

C 3

D 4

Solution

Correct Answer: Option C