By the age of two, Heidi could count to 40, draw pictures of people, and read books ________ for sevenyearolds.
——Can I join your club,dad? ——You can when you______a bit older.
This is a_______complicated(复杂的)problem.I don’t know how to solve it.
He came home______yesterday.
Asia is______the largest continent in the world.
_____explanation is necessary.