As for this problem concerning about a transition between sentences and paragraphs, the most probable and most likely to be the answer out of the options presented would be the third one which is a bridge.
A transition serves as a bridge between sentences and paragraphs. Though they create a divide between them, these transitions do not necessarily indicate that the divide is to cause to present that the two aren't connected to each other. A summary and introduction wouldn't do since a transition functions more and effectively between sentences and paragraphs.
Birthday is the subject of the sentence. This is because t<span>he subject of a sentence is the person, place, thing, or idea that is doing or being something.</span>
