What Observations of the Martian Surface Led Lowell to the Conclusion

What observations of the Martian surface led Lowell to the conclusion that intelligent life-forms existed on Mars?

A) melting icecaps, a network of linear features that look like canals, and varying dark surface marking assumed to be vegetation
B) geometrical structures and patterns that are apparently the remains of buildings and cities
C) sculpted mountains in the shape of humanoid heads, obviously carved to announce the presence of intelligent life to distant observers
D) lakes and rivers of water flowing from polar icecaps and detected by strong specular reflection of sunlight