We _______ start now to work for our project.

Option B is the correct answer.

The completed sentence is: “We better start now to work for our project.”

The term “better” in this context is a modal verb that is often used in informal spoken English. Modal verbs are auxiliary verbs that express necessity or possibility, and in this case, “better” is expressing a strong recommendation or advice.

When we say “We better start now,” it implies that it would be a good or beneficial idea to start now, and that there might be negative consequences if we don’t start now.