**Core Concept**
The evaluation of gonadotropins is crucial in assessing the reproductive axis, particularly in cases of infertility, menstrual irregularities, or suspected hypogonadism. Gonadotropin-releasing hormone (GnRH) stimulates the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary gland, which in turn regulate the function of the ovaries or testes.

**Why the Correct Answer is Right**
In a normal 28-day menstrual cycle, the day of evaluation is critical to assess the gonadotropin levels accurately. The LH surge typically occurs around day 14 of a 28-day menstrual cycle, which is crucial for ovulation. Measuring FSH and LH levels on this day can provide insights into the reproductive axis function. FSH levels are typically high during the follicular phase, stimulating the growth and maturation of follicles in the ovaries. LH levels, on the other hand, surge during the luteal phase, triggering ovulation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because LH levels are typically high during the luteal phase, making it unsuitable for evaluating FSH levels.
**Option B:** This option is incorrect because FSH levels are typically high during the follicular phase, making it unsuitable for evaluating LH levels.
**Option C:** This option is incorrect because LH levels are elevated during the mid-luteal phase, making it unsuitable for evaluating FSH levels.

**Clinical Pearl / High-Yield Fact**
In a normal menstrual cycle, the LH surge typically occurs around day 14, and FSH levels are high during the follicular phase. This knowledge is crucial in evaluating the reproductive axis and diagnosing conditions such as polycystic ovary syndrome (PCOS) or hypogonadism.

**Correct Answer: B. Day 3 (or 5-7) of a normal menstrual cycle, when FSH levels are typically high during the follicular phase.**