Prolactin is responsible for causing milk production in women.

Luteinizing hormone stimulates ovulation; the LH surge is caused by a positive feedback mechanism in which estrogen elicits the release of luteinizing hormone. The thyroid hormones generally regulate metabolism, and are themselves regulated by thyroid-stimulating hormone. Antidiuretic hormone and aldosterone indirectly regulate the acid-base balance of the body by adjusting reabsorption rates in the excretory system. The presence of these hormomes leads to water retention, which will dilute the blood. Oxytocin stimulates contractions during labor.

Antiduretic hormone (ADH) is alternatively known as vasopressin. It is secreted from the posterior pituitary gland and acts on the collecting ducts of the kidney to facilitate the reabsorption of water. Thus, ADH reduces the volume of urine formed, and increases blood volume.

In the passage it is stated that hCG is detected in the urine. In order to get there, the hormone must be filtered from the blood into the kidney tubules (via the glomerulus). The tubules must then not reabsorb all of it back into the blood; instead, the hCG must be allowed to leave in the urine. The other answer choices can be eliminated after consideration. The answer choice, 'hCG is also secreted by the mother', is wrong because hCG is only secreted by the fertilized embryo; if it was also secreted by the mother, the pregnancy test would not be effective because hCG could be detected in non-pregnant mothers.

In either case, the passage does not imply that the mother makes hCG. Answer choice, 'hCG does not enter the mother's bloodstream', can be eliminated because the passage directly states that hCG is released into the mother's bloodstream. The answer choice, 'The actions of progesterone are counteracted by hCG', is wrong because hCG works to maintain the corpus luteum, which secretes progesterone. If anything, hCG works to maintain the production and function of progesterone, not counteract it. 

Answering this question simply requires picking the answer choice that doesn't have anything in common with the others. Conditions in which specific antibodies are produced which might be tested for using the same technique are described in the passage. After all, antibodies are proteins, and monoclonal antibodies can be made to detect them. HIV infection can be detected by assaying for the antibodies against HIV.Arthritis can be detected by looking for antibodies against "self" proteins. Strep throat can be detected by directly assaying for the presence of bacterial proteins. The same technique which was used to detect hCG can be used in these instances. Tryptophan blood levels, however, cannot be determined using the same methodology. For one thing, tryptophan (an amino acid) does not elicit antibody production. Secondly, the actual levels of substances in the blood can't be detected by the type of test described in the passage. This test yields either a "present" or "not-present" result