ask sb do sth还是ask sb to do sth?

ask sb. to do sth 是固定的,但是在某些情况下有变化.
she is often heard to sing.
hear sb do sth是固定的
但是在次时改为hear to do

ask sb. to do sth.要求某人做某事

Ask sb to do!
我确定!
固定搭配,毫无疑问的!

ask sb do sth是对的
Ask so +动词原形为固定搭配

ask sb to do sth.
意思是要某人干。。。