Complete the amateur chef's embarrassing confession.

The smoke alarm started blaring _____ I was trying to microwave a whole watermelon.

The correct answer is while.

We use "while" to talk about two things happening at the same time, and it is followed by a subject and a verb (usually in a continuous tense, like "I was trying"). "During" is incorrect here because it must be followed by a noun, not a full clause.