Arun-on sentence is a sentence having two independent clauses
a. joined with words such as however or nonetheless.
b. with improper punctuation and without conjunctions.
c. with a period separating one clause from the next.
d. with a semi-colon separating one clause from the next.

A run-on sentence is a sentence having two independent clauses with improper punctuation and without conjunctions. The correct answer is option b. It is difficult to understand a run-on sentence because you cannot identify where to pause or stop and that the sentence does not have conjunctions which would help in the transition of clauses.

1: to try and stop the spread of communism

2: They thought college students should be drafted

3: president nixon removed american troops from vietnam