It is important for us       English well.

A．studying

B．study

C．to study

D．studied

颅骨骨折形成的过程是

A．颅骨内板断裂→内弯变形→外板断裂
B．颅骨外板断裂→内弯变形→内板断裂
C．颅骨内弯变形→内板断裂→外板断裂
D．颅骨内弯变形→内板、外板同时断裂
E．颅骨内外板同时断裂→颅骨内弯变形