The theory of suggests that the crust of the earth moves about on the upper mantle.

a : pangaea
b : convection
c : volcanism
d : plate tectonics

Which answer best describes an advantage of shipping goods by canal? a) most towns would rather have canals then noisy railroads b) goods could travel very fast downstream in the canal system c) traveling by boat is a much more relaxing way to transport goods. d) heavy loads of goods could travel by boat more easily then if pulled by horses.