could，let's，can't，don't，must

（1）We don't have enough time．

Let's

Let's

hurry up!
（2）

Don't

Don't

stand close to the tiger when you watch it．It's dangerous．
（3）-Is that girl your cousin Betty？
-It

can't

can't

be Betty．She went to London on holiday yesterday．
（4）I think this magazine

must

must

be Bob's because I see his name on it．
（5）I hear Alice is going to Beijing to study Chinese．

Could

Could

this be true？