The problem is _________ difficult ________ students can solve them.
-Are you going to the cinema_____ underground? -No. I am going there______ a bus.
If __________ bicycle is broken, _________ can use __________.
Mill Li asks Jill _______ look out ______the birds outside.
We are happy_______ you some ideas.
---Tomorrow is my ________ birthday. Would you like to come? ----Sure, I ______ .