It Was Originally Thought Questionable Whether a Crewed Lunar Landing

It was originally thought questionable whether a crewed lunar landing could take place because:

A) of the extreme temperatures on the lunar surface.
B) the lunar surface might be too soft to land upon.
C) of extreme levels of radiation from the decay of radioactive elements and the lack of a shielding atmosphere.
D) the low atmospheric pressure would adversely affect human beings.