Two experimental garden plots were each planted with the same number of tomato plants. Magnesium salts were added to the first plot but not to the second. The first plot produced 20 pounds of tomatoes and the second plot produced 10 pounds. Since nothing else but water was added to either plot, the higher yields in the first plot must have been due to the magnesium salts.
Which of the following, if true, most seriously weakens the argument above?

Question

Examsnet · Accepted Answer

Correct Answer is :  The two experimental plots differed from each other with respect to soil texture and exposure to sunlight.

GMAT Verbal Reasoning Practice Test 6