简述溪涧的特点。
参考答案：
①溪涧是曲折而长的带状水面；②有明显的宽窄对比；③溪中常有汀步、小桥、滩、点石等，且随流水走向有若隐若现的小路。
The doctor recommended that you swim after eating a large meal.
A wouldn't B couldn't C needn't D shouldn't
直通单座阀有何特点？
