instruction: Is the next sentence syntactically and semantically acceptable?

He sees often Mary.

response: unacceptable

instruction: Is the next sentence syntactically and semantically acceptable?

It was the man I saw that you wanted to meet.

response: acceptable

instruction: Is the next sentence syntactically and semantically acceptable?

John sang beautifully and a carol.

response: unacceptable

instruction: Is the next sentence syntactically and semantically acceptable?

Ellen was conferring.

response:
acceptable