A period and a semicolon both split two complete sentences. If both appear as choices for the same blank, you can usually cross them both out. The test will not ask you to pick the “better” of two legal STOP marks. Semicolons as a mark are in semicolons on ACT English.
Why both die
There is one right answer. If a period would work, a semicolon would also work, so neither can be the unique right choice. Look at the remaining options: a colon, a comma plus FANBOYS, a comma, or nothing. STOP versus GO is the frame, in STOP versus GO punctuation.
A colon is STOP only when the first side is a complete sentence and the second explains or lists. Colons are in colons on ACT English. FANBOYS with a comma is the other legal join, in FANBOYS.
The bottom line
Period and semicolon in the same question: drop both, then decide whether the sentence even needs a STOP mark.
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