Fill in the blanks with appropriate article:

I had been along this track many times and this was _________ first occasion when I hesitated.

the

The correct answer is OPTION 3 -- THE

I had been along this track many times, and this was the first occasion when I hesitated.

"The" emphasizes the definiteness and singularity of the "first occasion." It clarifies that this is the specific, already mentioned occasion when the speaker hesitated, setting it apart from any other times they might have been on the track.