1- I would attend the party, but I had to visit the doctor. Is this a correct complex sentence​

This is not a complex sentence. It is a compound sentence.

Explanation:

In the sentence we are analyzing here, the conjunction "but" is used to connect the two clauses. "But" is a coordinating conjunction, which means it is used to connect two independent clauses. When we join two independent clauses, what we have is a compound sentence. Independent clauses express complete thoughts, which means they can be read separately and still make sense.

That means this sentence is not a complex sentence. Complex sentences are joined by subordinating conjunctions, such as "because", "since", "although", etc. The clause that has the subordinating conjunction is a dependent clause, and it cannot stand alone as a sentence because it does not convey a complete meaning on its own. Example: I can't attend the party because I'm grounded.

answer: it's b friend !

explanation:

pretty easy question !