Possible answers:
a). moonlight;
b). looseness of dirt or compost;
c). permineralization;
d). water vapor;
e). fog;
f). The area was once underwater;
g). fissures of hot, acidic water;
h). contact between rocks;

Fact 1: Contact between rocks over long periods of time causes rocks to smooth. Fact 2: Smoothed, grooved and polished rocks are produced by glacial erosion. Given the two facts above, what is erosion?
Answer:
h).