71. The original building and loan associations were

organized as limited life funds, whose members made monthly payments on their share subscriptions, then taking turns drawing on the funds for home mortgages.

(A)  subscriptions, then taking turns drawing

(B)  subscriptions, and then taking turns drawing

(C)  subscriptions and then took turns drawing

(D)  subscriptions and then took turns, they drew

(E)   subscriptions and then drew, taking turns

The sentence speaks of a sequence of actions in the past:

shareholders made their monthly payments and subsequently took turns drawing on the funds. Choice C, the best answer, uses parallel past-tense verb forms to express this sequence. Choices A and B violate parallelism by using taking where took is required. The wording in D results in a run-on sentence and does not specify what the members took turns doing. Similarly, E does not specify what the members drew, and taking turns produces nonsense when combined with the rest of the sentence.

什么是run-on sentence?

Run-on Sentences 连写句

When a sentence consists of more than one clause, those clauses must be joined properly. It is never acceptable to hook two clauses together with a comma, as the "sentence" below does. That's called a run on sentence.

连写句：（错用逗号等）使两个或多个独立从句不正确地连在一起的句子

Wrong:        Nietzsche moved to Basel in 1869, he planned to teach classical philology.

There are a number of acceptable ways to fix a run on.

     1.  Make two separate sentences:

          Nietzsche moved to Basel in 1869. He planned to teach classical philology.

     2a. Change the comma to a semicolon:

          Nietzsche moved to Basel in 1869; he planned to teach classical philology.

     2b. Join the clauses with a semicolon and a transition word such as however or therefore.

          Nietzsche planned to teach classical philology; therefore, he moved to Basel in 1869.

Some common transition words are:

                           also             consequently

                           however         nevertheless

                           then             thus

                           besides          furthermore

                           hence           otherwise

                           moreover        still

                           therefore

3.  Join the two sentences with a coordinating conjunction: 并列连词

   Nietzsche moved to Basel in 1869, and he planned to teach classical philology

The coordinating conjunction are:

and       or

for        but

nor        yet

4a. If doing so is appropriate to the meaning, you can join the sentences with a subordinating conjunction: 从属连词Because Nietzsche planned to teach classical philology, he moved to Basel in 1869.

There are many subordinating conjunctions. Here are some of the most common ones

                           although           if

                           though            where

                           so                after

                           since              unless

                           while              therefore

                           because            than

                           until               thereby

                           before

4b. A special kind of subordinate clause is a relative clause. Relative clauses usually begin with relative pronoun.关系代词who, that, or which, and they relate the information in one clause to the subject of the other clause: Nietzsche, who planned to teach classical philology, moved to Basel in 1869.

一句话，GMAT SC中不可能出现两个独立的句子，对于解决SC RUN-ON错误足够了；

甚为详细，万分感谢古镯mm

"So" is another coordinating conjuction. There are total 7 of them. FANBOYS.

印象中用分号的也不少 不知算不算两个独立的句子

印象中用分号的也不少 不知算不算两个独立的句子