单选题 Be suspicious about water from other sources, such as ponds, streams, wells, tanks, water trucks or public standpipes.

【正确答案】 B

【答案解析】suspicious“可疑、猜疑”；doubtful“怀疑”；brave“勇敢”；quiet“安静”；careful“小心”。句意：不能相信水塘、河流、水井、运水船、运水车或公共水管子的水是清洁的。