1.He learns __ in the sea.（ ） A.to swim B.swimming c.to walk

1.选A learn to do swim 学游泳 句子意思：他在海里学游泳
2.选B 这题可以用排除法,看某人做什么事有两种表达：watch sb do sth 或者watch sb doing sth
这里只有B 是正确的搭配.
find sb do sth.就是讲发现某人做了什么事,是发现了整个过程,而find sb doing是发现某人正在做什么事,发现了一部分而已.
这里的语境是：我正在看孩子们玩,孩子们正在玩,所以选择B.

1. choose A because C&D are impossible, so don't even think about it. If you choose B, then you have to change "learns" in to "learned."
2. choose B because children is a plural noun, so A is incorrect. I don't know how to explain why not choosing C&D, but they are the wrong answers

A 学习做某事（to do表示目的，学习游泳）
B 宾语补足语，看着孩子们打球

learn to swim
playing