Trees can help ______ the air to keep it ______.[ ]A: clean, cleanB: cleaning, cleaningC: to clean;

题目简介

Trees can help ______ the air to keep it ______.[ ]A: clean, cleanB: cleaning, cleaningC: to clean;

题目详情

Trees can help ______ the air to keep it ______.
[     ]
A: clean, clean
B: cleaning, cleaning
C: to clean; cleaning
D: cleaning; clean
题型:单选题难度:中档来源:期末题

答案

A

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