STUDENT: I want invent 'time machine' if I were a inventor.
CORRECT: I want to invent "time machine" if I were a inventor.
EXPLANATION:
a. TO is used before a verb to make it infinitive.
b. When quoting, ' is used in British English while " is used in American English. Since we are practicing American English in here, we need to use ".
STUDENT: Because, I want to see my past, and my future.
CORRECT!
STUDENT: If I can return to past, I want to study more.
CORRECT: If I can return to the past, I want to study more.
EXPLANATION:
a. Past can mean a lot of things. If we are talking about the time before now, we need to make it specific by adding the definite article "the".
STUDENT: Therefore, I want to invent time machine.
CORRECT: Therefore, I want to invent a time machine.