Multiple choice

Directions: For this question, select the best of the answer choices given.

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 been due to the magnesium salts. Which of the following, if true, most seriously weakens the argument above?

  1. A small amount of the magnesium salts from the first plot leached into the second plot.

  2. Tomato plants in a third experimental plot, to which a high-nitrogen fertilizer was added, but no magnesium salts, produced 15 pounds of tomatoes.

  3. Four different types of tomatoes were grown in equal proportions in each of the plots.

  4. Some weeds that compete with tomatoes cannot tolerate high amounts of magnesium salts in the soil.

  5. The two experimental plots differed from each other with respect to soil texture and exposure to sunlight.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The argument incorrectly assumes magnesium salts caused higher tomato yields while ignoring other potential variables. Option E seriously weakens this by showing the plots differed in soil texture and sunlight exposure - factors that significantly affect plant growth. If the plots weren't comparable except for magnesium, the conclusion is invalid. Options A, B, C, and D don't address the core comparability issue: leaching would affect both plots (A), nitrogen fertilizer results don't weaken the magnesium conclusion (B), tomato types being the same supports rather than weakens (C), and weed intolerance doesn't challenge the magnesium effect (D).

Keep practicing — related questions