Modal verbs in logical assumptions

Сhoose the correct modal verb to rephrase the following sentence. I'm sure Susan was not writing a letter when I came in. Susan have been writing a letter when I came in.

Сhoose the correct modal verb to rephrase the following sentence. It's likely the secretary stayed late at the office yesterday. The secretary have stayed late at the office yesterday.

Сhoose the correct modal verb to rephrase the following sentence. I'm sure they will be leaving tomorrow. They be leaving tomorrow.

Сhoose the correct modal verb to rephrase the following sentence. I'm certain he hasn't arrived yet. He have arrived yet.

Сhoose the correct modal verb to rephrase the following sentence. Perhaps he is a doctor. He be a doctor.

Сhoose the correct modal verb to rephrase the following sentence. I'm sure John hasn't finished his homework. John have finished his homework.

Сhoose the correct modal verb to rephrase the following sentence. I'm certain they have been planning the project. They have been planning the project.

Сhoose the correct modal verb to rephrase the following sentence. I'm certain they are working together. They be working together.

Сhoose the correct modal verb to rephrase the following sentence. It's likely she is looking for a new flat. She be looking for a new flat.

Сhoose the correct modal verb to rephrase the following sentence. I'm certain my brother was having a shower when I rang. My brother have been having a shower when I rang.