Привет! Давай разберём ошибки и исправим предложения с "must" и "mustn't".
a. You must doing your homework.
Исправлено: You must do your homework.
b. You must to be careful when cutting food.
Исправлено: You must be careful when cutting food.
c. You mustn't shouting in the museum.
Исправлено: You mustn't shout in the museum.
d. He musts wear a school uniform.
Исправлено: He must wear a school uniform.
e. We mustn't to pick the flowers at the park.
Исправлено: We mustn't pick the flowers at the park.
f. You no must run at the swimming pool.
Исправлено: You mustn't run at the swimming pool.
g. We must looking both ways when crossing the road.
Исправлено: We must look both ways when crossing the road.
h. She mustn’t took toys to school.
Исправлено: She mustn't take toys to school.
Если что-то непонятно, спрашивай!