Fill in the blank with the most appropriate word. There is nothing we can do that _______ people from driving too fast.

The correct answer is: will stop.

The sentence is in the future tense, so the verb must also be in the future tense. The other options are in the past or present tense, which are not grammatically correct in this context.

• Is stopping is in the present continuous tense. This tense is used to describe actions that are happening at the moment of speaking. In this case, it would imply that people are currently being stopped from driving too fast, which is not the case.
• Stop is in the simple present tense. This tense is used to describe actions that happen regularly or repeatedly. In this case, it would imply that people are always being stopped from driving too fast, which is also not the case.
• Stopped is in the simple past tense. This tense is used to describe actions that happened in the past. In this case, it would imply that people used to be stopped from driving too fast, but they are not anymore, which is not the case either.

Therefore, the only option that is grammatically correct and makes sense in the context of the sentence is will stop.