为你解答.
（1）In the world, people sometimes communicate without （D:speaking）.
解释：speak表示说话的行为,tell是讲述.在介词without后用doing的形式.
(2)They greet each （A:other） by nodding their heads.
解释：each other,互相.
(3)After all, you cannot （B:shake hands） with a closed fist.
解释：shake hands,握手.手用复数形式,情态动词can后用动词原形.
指着人是失礼的.
It is rude to （point at） a person.
解释：point at,指着.强调所指的对象.
老师指着地图说：“这是北京”.
The teacher is （pointing to） the map and saying, "Here is Beijing."
解释：point to,指向.强调所指的方向.这里用现在进行时.