Choose the most suitable option to fill in the blank: We must do something soon before it ______(be) too late. A. was B. will be C. is D. has been

The correct answer is C. is.

The sentence is about the urgency of taking action before it is too late. The verb “to be” is used in the present tense to express this urgency. The other options are not as suitable because they do not express the same sense of urgency.

• Option A, “was,” is in the past tense. This would suggest that it is already too late to take action, which is not the meaning of the sentence.
• Option B, “will be,” is in the future tense. This would suggest that there is still time to take action, but the sentence expresses a sense of urgency that suggests that time is running out.
• Option D, “has been,” is in the perfect tense. This would suggest that something has already happened that makes it too late to take action, which is not the meaning of the sentence.

Therefore, the correct answer is C, “is.”