【单选题】By far the most common difficulty in study is simple failure to get down to regular concentrated work. This difficulty is much greater for those who do not work to a plan and have no regular routine o...
A.
the failure to keep to a routine of methodical and intensive work
B.
changing from one subject to another
C.
unwillingness to follow a systematic plan
D.
applying oneself to a subject only when one feels inclined