Distance decay in Russia is caused because of the separation of the
population and the resources by the __.
A. lakes
B. rivers
C. taiga
D. mountains

If I’m not wrong it would be D. mountains

Your answer is d. silli hope this ! : ) i left an explanation down below if you need it: a sill forms when hot magma squeezes between layers of rock to form a hardened sheet of rock. a sill is basically a tabular sheet intrusion between old layers of sedimentary rock, volcanic beds, or in the direction of foliation inherent in metamorphic rock. the word sill means a concordant intrusive sheet.