One of my close friends had a(n)________of this matter，so I had to explain it to him.[ ]

A．misunderstanding    

B．explanation

C．production  

D．result

“由浅入深，由易到难，由简到繁”体现了（）教学原则

A.巩固性

B.启发性

C.直观性

D.循序渐进