Here is the original item:
Citing writer's block as the reason
(A) that
she did not have her essay,
(B) Yao received
no sympathy from Professor Santos.
(C) Who will
only accept "breather's block" as a legitimate excuse for
late work.
You wanted to do this:
Citing writer's block as the reason that she did not have her
essay. Yao received no sympathy from Professor
Santos. Who will only accept "breather's block" as a legitimate
excuse for late work.
Adding a period after essay creates a fragment. Citing writer's block ... is a participle phrase. It cannot stand alone as a complete sentence.
You might want to review the rules.