A．Aspen trees are easier to transport.  
B．Aspen trees provide better wood for construction.           
C．Aspen trees provide less nutrition for beavers. 
D．Aspen trees have more overall value to beavers.

A．They generally prefer cutting down large trees to small trees.
B．They do not travel long distances to cut down large trees.
C．They will not cut down large trees of certain species.
D．They use large trees mainly for the purpose of building shelters.

A．Beavers are safer from their enemies at night.   
B．Beavers stay with their offspring during the daytime.
C．Looking for food at night requires less energy.   
D．Beavers face less competition for food from other animals.