Come in piease.Tom,you are late _______(to,of,for)school this morning.

for

for很固定的搭配

for
be late for 迟到

for
全句的意思是：请进，TOM，你这个早晨迟到了
be late for固定短语，迟到

for
be late for 迟到

Come in piease.Tom,you are late for (to,of,for)school this morning.
be late for...是固定搭配！