与十进制数511等值的十六进制数为（ ）。
A．1FF
B．2FF
C．1FE
D．2FE
参考答案：A
There are usually at least two _____ of looking at every question.
A．ways
B．directions
C．views
D．opinions
食管癌的等中心治疗的设野方法及其优点?
