Choose the correct modals/modal verbs of ability-can/can't/could/couldn't and an infinitive - to complete each sentence.

For example:

Susan (couldn't hear) the speaker because the crowd was cheering so loaudly.

1. The students_________that their teacher was very happy.
2. Chesca__________Mandarin fluently. She sounds like a native speaker.
3. Are you sure you put a tablespoon of brown sugar in my coffe? I______it!
4. The police searched the whole area for the burglars but the_______them.​