The sentence that contains a verbal phrase acting as a modifier is: Giving a presentation in front of my class, I suddenly developed sever stage fright.
Modifiers are optional elements in a phrase structure that even when removed, it does not affect the whole grammar of the sentence.
I'm not sure what the lesson is, but the answer that makes sense the most is number. Number because most lessons in subject-verb agreement concerns the singularity and plurality of the subject at hand
<span> 3(2x - 3) + 4(2 - x) = 0 6x - 9 + 8 - 4x = 0 2x - 1 = 0 2x = 1 x = 1/2. </span>
