The river near our school u________ to be clean,but now it becomes dirty.

问题描述:

The river near our school u________ to be clean,but now it becomes dirty.

正确来说你的 "become” 用错了..
正确的是: The river near our school used to be clean, but now it BECAME dirty.

used

used
短语知识:used to 意思是 “过去是……”
翻译:我们学校附近的河曾经是清澈的,但是现在变的浑浊了.