drop可用作名词“滴”；用作不及物动词“掉下，滴下”；用作及物动词“使掉(滴)下”。如：
a drop of blood一滴血；drop by drop/in drops一滴一滴地；drop from the tree从树上掉下来；drop to the ground 落在地上；drop the letter into the mailbox把信投进信箱；drop a handkerchief/stone掉下手帕/石头
习语：drop in 顺便拜访；drop in on sb.顺便走访某人；drop in at his school顺便拜访他的学校。
[应用]完成句子
①我看见一个苹果从树上掉下来。
I saw an apple______ _______ the tree.
②他们这样做是搬起石头咂自己的脚。
In doing so they are lifting a rock to _______ ________on their
feet.
③你路过的话，千万要来。
Do _______ _______ if you happen to be passing.
Key：
①drop，from ②drop， it ③drop， in
