Select the most appropriate option to fill in the blank.

The age of the participants ______ an important factor in this competition.

is

The most appropriate option to fill in the blank is is.

The word is is a singular present-tense verb that agrees with the subject age, which is singular. In this case, the sentence is saying that the age of the participants is an important factor in this competition. This means that the age of the participants is one of the things that will be considered when determining the winner of the competition.

The other options are not correct.

• Do is a plural present-tense verb that does not agree with the subject age, which is singular.
• Has is a singular present-tense verb that can be used with the subject age, but it would mean that the age of the participants has the property of being important. This is not what the sentence is trying to say.
• Are is a plural present-tense verb that does not agree with the subject age, which is singular.