Mark the letter A, B, C or D to indicate the correct answer to each of the following questions.

Câu hỏi

High levels of pollution can upset the ____________ of an ecosystem.

A. average

B. substance

C. reason

D. balance

Đáp án
D. balance

Câu hỏi thuộc Bài tập:

Ms. Dung Purple - Unit 9: Protecting the Environment - Vocabulary