From earliest times their energy had gone，first of all，into earnest toil.

From earliest times their energy had gone，first of all，into earnest toil.
A、..the difficult conditions had challenged people’s endurance.
B、..the most urgent task for people was to make a living by hard work.
C、..the unpleasant physical work had disappointed people there.
D、..people were very serious about how to use their energy.
正确答案：B