Yes, you can if you really want to:
private string @long;
The actual name of the variable (as reported by reflection etc) is just long
; the @
sign tells the compiler to ignore the fact that it's also a keyword.
I would very strongly advise against this, however.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…