A 2004 scientific drilling expedition in the Arctic found an abundance of Azolla fern spores in samples of 50-million-year-old material from the seafloor. Because the Azolla fern can grow only in freshwater, some scientists believe the spores originated in river deltas or lagoons and drifted into the Arctic Ocean. However, Brinkhuis believes that the fern grew in a once-verdant ocean. The sheer abundance of the spores makes it unlikely, by some accounts, that they would have originated elsewhere. It is possible that geologic forces at one point closed the straits connecting other oceans to the Arctic Ocean, so water from rivers feeding into it pooled and formed a surface layer of freshwater where the fern could survive. A later opening of the straits would have wiped out the fern.

The passage`s reference to "geologic forces" serves to indicate a mechanism by which

A rivers might have deposited large numbers of fern spores in the Arctic Ocean

No large numbers are mentioned in the passage

B freshwater lagoons might have formed close to the Arctic Ocean

out of scope. the spores might be originated into lagoons. The didnt formed close to the ocean

C the temperature of the Arctic Ocean might have risen

The temperature is out of scope

D water from other oceans might have become mixed with that of the Arctic Ocean

No mix is mentioned . Moreover from other oceans

E the Arctic Ocean might have become a suitable environment for ferns to grow in

The right one. The inference is in the red part

Regards