JULIE : I think it is brilliant colored clothes.
CORRECT : I think it is a brilliant colored clothing.
EXPLANATION : We use 'a' before the adjective 'brilliant' here because the article should go in front of the adjective if the noun is also being modified by an adjective. 'Clothes' is in plural form and your verb is in singular that is why your noun should also be singular.

JULIE : We will study about fungi today at science class.
EXPLANATION : This is correct. ☺

JULIE : I know that whales are mammals.
EXPLANATION : This is correct. ☺

JULIE :  I will gargle before I go to school today.
EXPLANATION : This is correct. ☺

JULIE : I should prevent them from fighting.
EXPLANATION : This is correct. ☺

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Hi Julie! Congratulations! You did an amazing job again with your homework today and you only have one grammar lapses today. Good job. As days pass by, you are always improving. Keep it up!

Happy Weekend Julie!

~Teacher Louise