Which of the following is a run-on sentence?

a.) holidays always go by too quickly since i get those days off.

b.) tomas was frustrated during class he forgot his book report.

c.) they danced for hours; they never felt remotely tired.

d.) the concert started and the music was incredible.

[1] on her way home from practice, rebekka found a gold man’s watch. [2] she wasn’t sure what to do. [3] there was no name engraved on the back. [4] looking at the gold links on the band, the watch seemed to rebekka to be expensive. [5] she felt badly that someone had lost such a nice watch. what is the best revision of the troublesome modifier in sentence 5?