Teaching and learning greatly from each other —they are two entirely different processes.

问题补充：

Teaching and learning greatly from each other —they are two entirely different processes.

A. differ

B. disagree

C. compare

D. transform

答案：

(答案→)A. differ

B. disagree

C. compare

D. transform

解析：句意：教与学彼此之间是不同的，它们是两个完全不同的不同的过程。Differ相异；disagree不同意；compare比较；transform转变。根据句意故选A。