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"Gustave Eiffel created the statue's internal structure, and his engineering method is used today..'' is a compound sentence.
A compound sentence contains two independent clauses. An independent clause is one that has a proper meaning without the other clause.
These independent clauses are joined together using suitable conjunction such as: and, yet, for, so, and, & many more.
In the given sentence, "Gustave Eiffel created the statue's internal structure" and "his engineering method is used today" are two independent clothes, and each makes sense without the other.
They have been joined together using the conjunction 'and.'
On the other hand, a simple sentence consists of only one clause It has only one subject, the predicate. It is only one independent clause.
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