Final answer:
After three weeks of a male bodybuilder taking daily testosterone injections, you would observe increased muscle mass, increased sex drive, and decreased levels of GnRH, LH, and FSH due to the negative feedback loop in the endocrine system. Hence, all listed effects (A, B, C, D) are correct.
Step-by-step explanation:
If a male bodybuilder starts taking injections of testosterone, an anabolic steroid, on a daily basis, after three weeks, you would expect to observe several effects. One of the key changes would be an increased muscle mass, as testosterone is responsible for muscle building. Additionally, you would also likely notice an increased sex drive, which is another physiological function of testosterone.
Importantly, due to the negative feedback loop in the endocrine system, increased levels of testosterone would inhibit the production of GnRH (gonadotropin-releasing hormone), along with LH (luteinizing hormone) and FSH (follicle-stimulating hormone) by the hypothalamus and pituitary gland. Therefore, taking testosterone injections can lead to decreased levels of GnRH, LH, and FSH.
In conclusion, the correct answer to this question would be E) All of the answers are correct since all the listed effects are typically seen with the use of anabolic steroids like testosterone.