19.China has warned America that it_____be responsible for its arms sale to Taiwan.
Lin Tao can't be at home. I saw him _______here a few minutes ago.
Every day I spend two hours _______my homework.
Jack's brother doesn't work so _________as Jack.
In our exam, the____ careful we are, the ______mistakes we’ll make.
A ___school boy, LiLida, first tried to swim across the Qiongzhou Channel in June, 2000.