Critical Reasoning

After a decline in stockbroker training, errors made in the country's incredibly competitive stock exchanges have gone up by 30 percent. To offset this difficulty, more of the purchase and sale opportunities at the most competitive stock exchanges should be assigned to professional stockbrokers.

Which of the following, if true, casts the most doubt on the effectiveness of the solution proposed above?

A The primary reasons for errors made in the country's most competitive stock exchanges are computer malfunctions and unexpected shifts in the stock market.
B After stockbroker training began to decline, the amount of stock transactions conducted has gone up by 30 percent.
C More than 55 percent of the purchase and sale opportunities at the most competitive stock exchanges are set aside for professional stockbrokers.
D When a quiet regional stock exchange tripled its assignment of purchase and sale opportunities, the amount of documented errors went down by 45 percent.
E After the training decline the average error amount in the country's most competitive stock exchanges has tripled.

Like most weaken questions, this question relies on finding the assumption.

All that the argument says is that after a decline in training, errors increased by 30 percent. It is left for the reader to assume (as does the author) that the lack of training is the cause of the errors. Answer choice (A), however, reveals the real reason for the errors -- computer malfunctions and unexpected shifts, two things that have nothing to do with a lack of training. Accordingly, the proposed solution remains in doubt.