she is sitting under the tree.
她正坐在树下.
主语:she
谓语:is sitting
介词短语作状语:under the tree.
She is sitting under the tree.此句话的意思是“她正坐在树下.”
is sitting作谓语,说明动作状态;under the tree介词短语作状语,修饰动作is sitting,表示地点.
介词短语是可以做表语的,
如She is under the tree.她在树下.under the tree介词短语作表语,说明She的状态.