气缸套腐蚀磨损的表面特征是产生（ ）。 A.
擦伤撕裂 B.
纵向拉痕 C.
局部剥落 D.
裂纹

A．The statement of research questions
B．Make the questions specific and small
C．Turn questions into research variables and assumptions
D．Turn problems into research design