Question

which is a compound - complex sentence?
while they were walking on campus, dwayne admired the buildings and michelle imagined attending classes in this beautiful place.
daily exercise is beneficial to your health, therefore you must take several precautions to avoid injuries.
our experienced tour guide, who grew up in the area, directed us toward some amazing local scenes.
the electronic merchandise was defective, as it had been severely damaged during shipment.

Explanation:

A compound - complex sentence has at least two independent clauses and at least one dependent clause.

• For the first option: "While they were walking on campus" (dependent clause), "Dwayne admired the buildings" (independent clause), and "Michelle imagined attending classes in this beautiful place" (independent clause). So it has 1 dependent and 2 independent clauses, fitting the compound - complex structure.
• The second option: "Daily exercise is beneficial to your health" (independent) and "you must take several precautions to avoid injuries" (independent) are joined by "therefore", but there's no dependent clause, so it's a compound sentence.
• The third option: "who grew up in the area" (dependent clause) and "Our experienced tour guide directed us toward some amazing local scenes" (independent clause), so it's a complex sentence.
• The fourth option: "as it had been severely damaged during shipment" (dependent clause) and "The electronic merchandise was defective" (independent clause), so it's a complex sentence.

Answer:

While they were walking on campus, Dwayne admired the buildings and Michelle imagined attending classes in this beautiful place.