Is this a complete sentence, a sentence fragment, or a run-on sentence?

wondering about the distances between planets in our solar system.

a.
sentence fragment

b.
complete sentence

c.
run-on sentence

Part a which statement best describes a central idea in this narrative? in times of tragedy, it is difficult to determine how best to be of service. in times of crisis, people prefer to be alone. young people tend to look to older people to take action in times of tragedy. when people publicly commit to being of service, they are more likely to follow through. part b which detail from the text best to shape the central idea in part a? "'i thought you might have too much going on already. i saw everyone post online.' martin said, 'i don’t think anyone wanted to be in the way today, so i’m glad you came.'" "finally, he said, 'i don’t know what to do. i guess i should tell him to let me know if he needs anything, but that doesn’t feel like enough.'" "he wondered how many people would actually show up to out and how many would simply hope that enough others did." "he explained to her that martin’s mom had died, and told her how he felt about his friend’s loss. 'what do you plan to do for him? ' his mother asked."