Which of the following sentences is grammatically incorrect?

Question

Quizplus · Accepted Answer

"My boss is unable to remember names and he always calls me Samuel instead of Saul" is grammatically incorrect because it is a run-on sentence.
Run-on sentences are when two or more complete sentences are written as one sentence. Run-on sentences can be fixed by adding a dash (-), a semicolon (;), or a colon (:) between the two sentences. You could also add a coordinating conjunction with a comma (, but) or make them two separate sentences with a period (.).
Any of these would be considered correct:
My boss is unable to remember names - he always calls me Samuel instead of Saul.
My boss is unable to remember names; he always calls me Samuel instead of Saul.
My boss is unable to remember names: he always calls me Samuel instead of Saul.
My boss is unable to remember names, so he always calls me Samuel instead of Saul.
My boss is unable to remember names. He always calls me Samuel instead of Saul.

Which of the Following Sentences Is Grammatically Incorrect