prep1-77 therefore用法

77。Scientists
            have
            found
            signs
            that moving
            water
            changed
            the
            chemical
            makeup
            of
            the
            surface
            of
            Mars
            in recent
            eras, therefore
                concluding
                that
                its
                crust
                is
                harboring
                up
                to
                three
                times
                as
                much
                water
                than
                was previously
            thought.

(A)
            eras, therefore
            concluding
            that
            its
            crust
            is
            harboring
            up
            to
            three
            times
            as
            much
            water
            than
            was

(B)
            eras, therefore
            concluding
            that
            the
            planet's
            crust
            harbors
            up
            to
            three
            times
            as
            much
            water
            or
            more
            as
            was

(C)
            eras
            and
            have
            therefore
            concluded
            that
            the
            planet's
            crust
            harbors
            up
            to
            three
            times
            as
            much
            water
            as

(D)
            eras
            and
            they
            have
            concluded, therefore, that
            its
            crust
            harbors
            up
            to
            three
            times
            as
            much
            water, or
            more, than

(E)
            eras
            and
            concluded, therefore, that
            the
            planet's
            crust
            is
            harboring
            up
            to
            three
            times
            more
            water
            as
            was

不知道A, B中的therefore用法是否正确？therefore作为副词不能代替连词引导句子（同then,等），那么应该也不能代替介词引出分词短语吧？！

我查了nytimes.com，大部分的例子都是...., and therefore, .....，或者....., therefore,....

当然也有个别的用到..., therefore v-ing....（难道therefore作为副词修饰后面的动名词？好奇怪的说）

请教一下NN们，GMAT中therefore的用法到底如何，谢谢了

Therefore確實沒有連接詞功能，但是本題是一個伴隨狀語(應該沒說錯)的句型，也就是把原來

"and therefore concluded...."簡化為"therefore concluding...."分詞型態出現，因此是不需要連接詞的。

本題主要還是考as....as這個點。