The answer to your question would be that the option that is an example of a complex sentence is the following one: Processsed foods should be avoided because they can lead to serious health problems. That is, the correct option would be C.
A complex sentence has one independent clause and at least one dependent clause. Independent clauses, unlike dependent clauses, can stand alone as a sentence as they represent a complete thought. You can see this in the following examples.
a) Processed foods should be avoided (independent clause)
b) *Because they can lead to serious health problems (dependent clause)
Nature is those things acquired by genetic or hereditary influences. Nurture on the other hand is those things that are influenced by the environment we live in. ... An example of this debate is whether high blood pressure and obesity is a health risk that is passed genetically from parent to child.
