Select the most appropriate option to fill in the blank and make a grammatically correct sentence.

I was walking along the street when suddenly I ________ footsteps behind me.

heard

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

The sentence is in the past tense, and the verb "to hear" needs the past tense form. The past tense form of "to hear" is "heard."

The other options are not grammatically correct.

• Hear is the present tense form of the verb "to hear." It is not the correct form to use in this sentence, because the speaker is talking about something that happened in the past.
• Hearing is the gerund form of the verb "to hear." It is not the correct form to use in this sentence, because gerunds are not used to describe actions that happened in the past.
• Was hearing is the past progressive tense form of the verb "to hear." It is not the correct form to use in this sentence, because the speaker is not talking about an action that was happening over a period of time in the past.