The are 7 continents.
Continents are Asia, Africa, Antarctica, Europe, Oceania, North America and South America.
They have lots of countries.

Mary: There are 7 continent.
Corrections: The are 7 continents.
Explanation: You have to put an -s because it's plural, It is many.

Mary: Continent are Asia, Africa, Antarctica, Europe, Oceania, North America and South America.
Correct: Continents are Asia, Africa, Antarctica, Europe, Oceania, North America and South America.
Explanation: You have to put an -s because it's plural, It is many.
 
Mary: They are have a lot of countries.
Correct: They have lots of countries.
Explanation: No need to put are because it is not necessary to your sentences. Lots is already considered as plural already.

note: Homework spells like this.
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Hello Mary ^^

Good job for this homework. Keep it up! ^^

Love,

Teacher Mary  :)