Fact 1: Damming a river can cause a lake to form. Fact 2: The beavers live on this side, and create dams. Given the two facts above, what animal can cause a lake to form?

Available options:
a). trout;
b). Beavers;
c). Clams;
d). salmon;
e). Lake Trout;
f). Sea Otters;
g). Dam;
h). mussels;
Answer:
b).