either과 neither의 차이점?

[익인이]

안녕하세요 선생님!!

George has not completed the assignment yet, and Mark hasn't either.

이 지문에서 저는 either이 아니라 neither인 줄 알고 틀렸는데

either과 neither의 차이점이 무엇인가요..?

[David]

안녕하세요 ^^

not either = neither 입니다.

George has not completed the assignment yet, and Mark hasn't either. (O)
George has not completed the assignment yet, and neither has Mark. (O)

늘 웃으면서
힘차게 홧팅 !!!