一侧牙齿缺失，对侧牙舌侧倒凹过大者，应将
A．模型向前倾斜B．模型向后倾斜C．模型向左倾斜D．模型向右倾斜E．模型向有牙侧倾斜
参考答案：E
He practices _______ English if he can.[ ]
A. speaking
B. to say
C. to talk
D. to tell
Very long，complex expressions in program are difficult to write correctly and difficult to（）.
A．defend
B．detect
C．default
D．debug
