All of the following sentences are complex except

a) even though acid rain can have damaging effects, few people know much about it.
b) acid rain has been studied as an environmental issue by the government since the 1970s.
c) since they erode statues and corrode steel structures, the chemicals in acid rain are harmful.
d) since the industrial revolution began, emissions of sulfur dioxide and nitrogen oxide have increased.

B) Acid rain has been studied as an environmental issue by the government since the 1970's.

Explanation: All of the following sentences are complex EXCEPT Acid rain has been studied as an environmental issue by the government since the 1970's. "As an environmental issue" is a prepositional phrase, which makes the sentence a simple sentence. All of the other sentences contain one independent clause and one dependent (or subordinate) clause.

a. they have shared matter.

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