Which of the following is a run-on sentence?

a. the barn has a funny smell; maybe it's coming from the cows.
b. the barn has a funny smell. maybe it's coming from the cows.
c. the barn has a funny smell maybe it's coming from the cows.
d. the barn has a funny smell, and vern thinks maybe it's coming from the cows.

Me asap it's an e2020 test and it's timedread the rough draft of a student's conclusion to anargumentative editorial.(1) year-round schooling would student achievement.(2) not so much information would have to be crammed intonine months. (3) furthermore, the elimination of long breaks, particularly summer break, would significantly reduce"learning loss" and the additional time wasted at thebeginning of each academic year to reteach previouslylearned material. (4) it is clear that year-round schooling students learn and retain more. (5) the united statesis not the only country to experiment with a year-roundschool schedule. (6) although many still claim that evidenceabout year-round school and its link to higher achievement isinconclusive, these people need to open their eyes and seethat students in these schools consistently score higher oncertain assessments than students who attend schools withtraditional nine-month calendars. (7) it is about time that wereplaced our outdated and inefficient school calendars. what revision would most strengthen sentence 1?