In which decade were the first important laws passed to decrease water pollution?
a 1950
b 1960
c 1970< <
d 1980

Which of the layers of the earth has the following three characteristics? i. it is made of molten rock. ii. it has currents that are constantly moving. iii. earth’s plates float on top of its currents.

What causes heat transfer in fluids

Read the article about the fraser river, one of the most important rivers in canada. what is the most important species of fish in this river? why are the numbers of these fish declining?