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'

this is b. how railways dealt with people riding the trains without paying