INFINITIVE AFTER QUESTION WORDS
These verbs: ask, decide, explain, forget, know, show, tell, understand, can be followed by a question word such as where, how, what, who, when or 'whether' + the 'to-infinitive'.
- She asked me how to use the washing machine.
- Do you understand what to do?
- Tell me when to press the button.
- I've forgotten where to put this little screw.
- I can't decide whether to wear the red dress or the black one.
The question word Why is followed by the zero infinitive in suggestions:
- Why wait until tomorrow?
- Why not ask him now?
- Why walk when we can go in the car?
- Why not buy a new bed for your bedroom?
- Why leave before the end of the game?
- Why not spend a week in Beirut and a week in Baghdad?