Even before telescopes were invented, humans were interested in astronomy.

A) Simple

B) compound

C) complex

D) compound-complex

18. Halley's comet should return in the year 2061.

A) Simple

B) compound

C) complex

D) compound-complex

The first sentence is an example of (C) complex sentence because it contains one independent clause and at least one dependent clause. The independent clause is: "humans were interested in astronomy". Dependent clause is: 'even before telescopes were invented' (dependent because it cannot stand on its own'.

Second sentence is an example of (A) simple sentence because there is only one subject 'Haley's comet'