The question is testing verb usage. The three women have received in the past and continue to receive support from labor. Thus we need to use present perfect to show something which continues from the past and still is happening.
This leaves options A and C on the table. C is better A has two issues - unqualifying is used incorrectly and the GMAT prefers not to use possessives as much as possible.
Now the specific question, E uses "are" which means they are getting support now but the past is discounted. Another issue is "support of" is better than "support by"
Hope this helps!














