I.词语辨析：
1、through / across / past / over
through：穿过，指动作是在某一空间进行的。
e.g. We walked through the forest and reached the mountain village.
across：横穿，表示动作是在某一物体的表面进行。
e.g. Can you see anything walking across the playground?
past：经过，指从某一物体的旁边经过。
e.g. I went past their classroom and found them working hard.
over：越过，指从上方跨越而过。
e.g. He ran faster and faster, jumped over the small river and disappeared in the trees.
Planes flew over the city many times a day.
2、clean / clear
clean：adj. 干净的、清洁的，与dirty相反。
e.g. Please wear clean clothes and polished shoes.
vt.把……擦干净
