We will be late if we . . . . . . . . not leave now.

The correct answer is: A. do

The sentence is in the present tense, so the verb “leave” should also be in the present tense. The other options are not in the present tense.

• Will is the future tense of “will”. It is used to talk about things that will happen in the future.
• Shall is the formal version of “will”. It is used to make requests or give orders.
• Did is the past tense of “do”. It is used to talk about things that happened in the past.

Here is a rewritten version of the sentence using the correct verb:

We will be late if we do not leave now.