Which of the underline  expressions is  the hedging of the following sentences.
For our present purpose, it is useful to distinguish two kinds of chemical reaction, according to whether the reaction releases energy or requires it.

A． For our present purpose, it is useful to distinguish two kinds of chemical reaction, according to whether the reaction releases energy or requires it.
B． For our present purpose, it is useful to distinguish two kinds of chemical reaction, according to whether the reaction releases energy or requires it.
C． For our present purpose, it is useful to distinguish two kinds of chemical reaction, according to whether the reaction releases energy or requires it.
D． For our present purpose, it is useful to distinguish two kinds of chemical reaction, according to whether the reaction releases energy or requires it.