It's difficult to live in a foreign country, ______ if you can't understand the language there.
A:exactly
B:naturally
C:usually
D:especially
如图,一座石拱桥是圆弧形,其跨度(AB长)为24米,半径为13米,则拱高(CD长)为( )
“五水共治,治污为先”是我省提出改善生态环境的一项重要政策。为了防止水体污染,你认为下列措施中不可行的是( )