1. I will leave the party early because I must studying for my exam.

• Correction:  (I must --> I must study)

1. I stayed up late last night because I mustn't go to school on Sunday.

• Correction:  (I mustn't --> I don't have to / I mustn't go)

1. We ought to not play football as it's raining outside.

• Correction:  (ought to not --> ought not to)

1. You mustn't to drive a car if you don't have a licence.

• Correction:  (mustn't to --> mustn't drive)

1. If you want some useful advice, you have better talk to your parents about your problem.

• Correction:  (have --> had)

1. I had stay at home 3 days due to snowing heavily.

• Correction:  (had stay --> had to stay)

1. Because of his poverty, he has to struggling to make ends meet.

• Correction:  (struggling --> struggle)

1. According to the rules of this game, you had better not drop the ball.

• Correction:  (had better --> better not)

1. If you want to get a higher mark in the next test, you have better put more effort into vocabulary.

• Correction:  (have to do --> had)

1. We shouldn't make an appointment with this doctor. You can see him whenever you want.

• Correction: No error.

1. Look at the sky, it is going to rain. Thus, you must bring along a raincoat.

• Correction: No error.

1. I ought to go home now because I don't want to walk in the dark.

• Correction:  (ought --> ought to)

1. As our teacher said yesterday, we ought to not worry about the mid-term test. Take it easy.

• Correction:  (ought to not --> ought not to)

1. This competition is optional, so we not have to take part in it.

• Correction:  (not have --> don't have)

1. Despite having a little chance to win, you should give up your dream of becoming a star.

• Correction: No error.

1. The professor told me that we should give this assignment in by Thursday at the latest.

• Correction: No error.

1. What you should do now is to make slides for the presentation tomorrow as we have a little time left.

• Correction: No error.

1. You have to apply for this position as soon as possible since it has only three vacancies.

• Correction: No error.

1. Ms. Anna will give a fascinating lecture at 8 a.m., so you should be here at 7.45 to check in.

• Correction: No error.

1. My advice is you have to consider carefully before making the final decision.

• Correction: No error.

#yuno