The identifier of the variable should be

A meaningful element consisting of underscores, letters and numbers beginning with underscores, and no spaces.

If it is a constant. .

Then you should choose D above.

a

Chinese, 00 1 1 is legal, b.

middle

456 is legal, C.

999 is legal.

0x generally stands for 16 hexadecimal number, 0 generally stands for octal number, and f generally stands for floating point.