More has been learned since 1945 about the chemical changes in t

More has been learned since 1945 about the chemical changes in the body than in all human history before （）time.
A、in
B、that
C、which
D、the
【正确答案】：B
【题目解析】：这里指的是在1945年之前的那个时期，并有强调之意。选项B是正确的。