Final answer:
Fertilization is most likely to occur after LH levels peak and begin to decline, which is around the time of ovulation, when the egg is released and can be fertilized.
Step-by-step explanation:
According to the graph and information provided about the menstrual cycle, fertilization is most likely to occur after luteinizing hormone (LH) levels peak and begin to decline, around the time of ovulation. Ovulation is stimulated by a sudden rise in LH levels, known as the LH surge, which occurs approximately on day 14 of a 28-day cycle. This surge results in the follicle rupturing and releasing its egg. After ovulation, the levels of estrogen drop as the non-ruptured follicles degenerate.
The correct answer to the question about when fertilization is most likely is b. after luteinizing hormone (LH) levels peak and begin to decline. This is because the egg is released during this time and is available to be fertilized by a sperm in the fallopian tube.
It is also important to correct some misconceptions: Menstruation occurs after progesterone levels drop, not just after LH and FSH levels peak. Additionally, estrogen levels rise before ovulation, stimulating the release of LH, which leads to the egg's release.