方位介词on, over, above的用法辨析

A.介词on表示一物放在另一物上面，两者紧贴在一起，如：The book is on the table.

B.介词over表示一种垂直悬空的上下关系，即“在…上方”，如：Is there any bridge over the river?

C.介词above表示一般的“高于…”，“在…之上”，如：There was an electric clock above his bed.

方位介词under与below的用法辨析

A.介词under是over的反义词即“在…下方”，如：They were seen under the tree.

B.介词below是above的反义词即“低于…”，“在…之下”，如：They live below us.