They have been doing morning exercises they up.
A. since, got
B. for, get
C. since, get
D. for, got
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(答案→)A. since, got
B. for, get
C. since, get
D. for, got
解析：根据since后面跟从句或表示时间点的短语，for后面跟表示时间段的短语的用法和they可知，后面应该是从句，故应该排除BD；又根据since后面的从句用过去时，可知本题应该选A。