The correct answer is C. interesting.
The chief guest’s speech was so interesting that I was all ears. This means that the speech was so engaging and captivating that I was completely focused on what the speaker was saying. I was not distracted by anything else, and I was eager to hear what the speaker had to say.
The other options are not as accurate. Option A, intricate, means complex or difficult to understand. This does not seem to be the case with the chief guest’s speech, as the speaker was able to hold the audience’s attention. Option B, interminable, means long and boring. This also does not seem to be the case with the chief guest’s speech, as the speaker was able to keep the audience engaged. Option D, indeterminate, means uncertain or undecided. This does not seem to be the case with the chief guest’s speech, as the speaker seemed to have a clear message that they wanted to convey.