Questions about English Gramma

Question 1:
Susan plays the violin very badly. (correct)
Susan plays violin very badly. (false. "The" should be added before "violin" since violin is a musical instrument)

Question 2:
Does Susan go to school on Saturdays? (correct. Because "Saturdays" is in plural form, it has the same meaning as "every Saturday")
Does Susan go to school on Saturday? (correct. In this case, "Saturday" only means the coming "Saturday", but not "every Saturday")

Question 3:
Do they smoke? (Correct. It describes their habits as it is in simple present tense)
Are they smoke? (false. Grammatical mistake)
Are they smoking? (correct. It means "are they smoking" at this moment. It tells the action of them)

Question 4:
Who lives here? (correct. more informal saying)
Who is living here? (correct. Same meaning as the previous one)
Who is living in here? (correct. Same as the previous one)

Question 1:
Susan plays the violin very badly. ---- Correct.
Susan plays violin very badly. --- Wrong, "the" should be used before musical
instrument, in this sentence, it is "violin".

Question 2:
Does Susan go to school on Saturdays? --- Correct. "Saturdays" in this case
means every Saturday.
Does Susan go to school on Saturday? --- Wrong. It asks about Susan's habit
and not a specific occasion, therefore "Saturdays" should be used instead of
"Saturday"

Question 3:
Do they smoke? --- Correct. It asks whether they have the habit of smoking.
Are they smoke? --- Wrong
Are they smoking? --- Correct. It asks whether they are smoking at the moment.

Question 4:
Who lives here? --- Correct.
Who is living here? --- Correct in grammar but we usually use the first one if we
want to know who lives there habitually.
Who is living in here? --- Wrong

Question 1:
Susan plays the violin very badly Correct.
Susan plays violin very badly. Wrong

Question 2:
Does Susan go to school on Saturdays? Correct
Does Susan go to school on Saturday? Correct

Question 3:
Do they smoke? Correct
Are they smoke? Wrong
Are they smoking? Correct

Question 4:
Who lives here? Correct
Who is living here? Correct but we seldom put it this way
Who is living in here? Wrong

Question 1:
Susan plays the violin very badly.---------wrong
Susan plays violin very badly.--------------correct

Question 2:
Does Susan go to school on Saturdays?-----wrong
Does Susan go to school on Saturday?-------correct

Question 3:
Do they smoke?--------correct
Are they smoke?--------wrong
Are they smoking?------correct

Question 4:
Who lives here?------wrong
Who is living here?------correct
Who is living in here?-------corrrect