og sc 111关于so that 前能否加逗号问题

joannahope

111. A mutual fund having billions of dollars in assetswill typically invest that money in hundreds of companies, rarely holding more than one percent of the shares of any particularcorporation.

(A) companies, rarely holding more than one percent
(B) companies, and it is rare to hold at least onepercent or more
(C) companies and rarely do they hold more than onepercent
(D) companies, so that they rarely hold more than onepercent
(E) companies; rarely do they hold one percent or more

关于at least one percent or more  问题我就不赘述了 ，之前有很多讨论了 现在问一下C选项 虽然一早能排除掉 但是头一次见到so that 前面加逗号的  在百度上查了一下  这种用法没有错误  表结果的时候说是可以用的 但是在表目的的时候是不可以用 不知道这种用法在Gmat 中能否得到认可  我只是在网上查的没有朗文之类的查证 希望大神给解答一下