A group of scientists studying calcium metabolism in laboratory rats discovered that removing the rats’ parathyroid glands resulted in the rats’ having substantially lower than normal levels of calcium in their blood. This discovery led the scientists to hypothesize that the function of the parathyroid gland is to regulate the level of calcium in the blood by raising that level when it falls below the normal range. In a further experiment, the scientists removed not only the parathyroid gland but also the adrenal gland from rats. They made the surprising discovery that the level of calcium in the rats’ blood decreased much less sharply than when the parathyroid gland alone was removed.
Which one of the following, if true, explains the surprising discovery in a way most consistent with the scientists’ hypothesis?
(A) The adrenal gland acts to lower the level of calcium in the blood.
(B) The adrenal gland and the parathyroid gland play the same role in regulating calcium blood levels.
(C) The absence of a parathyroid gland causes the adrenal gland to increase the level of calcium in the blood.
(D) If the adrenal gland, and no other gland, of a rat were removed, the rat’s calcium level would remain stable.
(E) The only function of the parathyroid gland is to regulate the level of calcium in the blood.
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Regards, S

I will go with 'A'

Removed Parathyroid gland - calcium level drops --> Parathyroid helps to regulate the calcium level in the blood.

Removed both Parathyroid & adrenal gland-the rate of decrease is less, so the conclusion is that adrenal gland lowers the calcium level

idiot ! idiot ! idiot ! it is A) !

Ok got it eventually.
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Regards, S

Fact: Removing P gland results in lower levels of calcium.
Hyperthesis: P gland regulate calcium level by raising it when it is low.
Fact: Remobing both P gland and A gland results in less sharply decline in calcium level.

Ask for explanation.

(A) The adrenal gland acts to lower the level of calcium in the blood.
This is it. P raises it and A lowers it. With A not B result would be the level is lowered. Without both nothing is there to lower it or increase it so it might not change that much.

(B) The adrenal gland and the parathyroid gland play the same role in regulating calcium blood levels.
If they both raises calcium level, without both the level should decrease even more.

(C) The absence of a parathyroid gland causes the adrenal gland to increase the level of calcium in the blood.
That would result in a higher level of calcium in the first case than the second.

(D) If the adrenal gland, and no other gland, of a rat were removed, the rat’s calcium level would remain stable.
It doesn't explain the discovery.

(E) The only function of the parathyroid gland is to regulate the level of calcium in the blood.
It still doesn't explain the discovery.