Question

Sentence structure. 1. In 1984, Byron Lichtenberg, who is a biomedical engineer, became a member of a spacecraft crew. 2. Lichtenberg discovered that dealing with zero gravity was difficult.

Answer 1

A simple sentence has only one independent clause. A compound sentence has at least two independent clauses. A complex sentence has one independent clause and at least one dependent. A compound-complex sentence has at least two independent clauses and one dependent.
Having this in mind, 1. is a complex sentence, and 2. is also a complex sentence.