The correct answer is A) can. The modal verb "can" can indicate possibility.

Modal verb 'can' is used to show possibility.

Modal verbs are a category of auxiliary verbs that are used to express various meanings such as ability, permission, obligation, and possibility. In this case, the modal verb 'can' is used to indicate possibility.

Explanation:
The modal verb 'can' is often used to express the idea that something is possible or that someone has the ability to do something. It is used to show that there is a chance or likelihood of something happening.

Example sentences:
1. I can go to the party tonight if I finish my homework in time.
2. It can rain tomorrow, so don't forget to bring your umbrella.
3. She can speak Spanish fluently.
4. They can win the match if they play well.

In each of these sentences, the modal verb 'can' is used to indicate the possibility of something happening. It suggests that there is a chance or ability for the action to occur.

Other modal verbs:
While 'can' is the modal verb primarily used to show possibility, there are other modal verbs that can also express possibility to varying degrees. These include 'might', 'could', and 'may'.

Example sentences:
1. It might rain tomorrow, so I'll bring my raincoat.
2. She could come to the party if she finishes her work early.
3. He may be able to solve the problem if he tries.

These modal verbs also imply the idea of possibility, but they may convey different levels of certainty or likelihood compared to 'can'.

In conclusion, the modal verb 'can' is used to show possibility. It suggests that there is a chance or ability for something to happen. Other modal verbs like 'might', 'could', and 'may' can also express possibility, but 'can' is the primary modal verb used for this purpose.