LH surge defines mid-cycle ovulation peak

Steps:

• Recall standard menstrual cycle phases: follicular, ovulation, luteal.
• Identify graph features: rising levels in follicular phase, sharp mid-cycle peak, then decline.
• Match peak timing to ovulation trigger around day 14.
• Confirm hormone with pre-ovulatory surge: luteinizing hormone (LH).

Why B is correct:

• LH concentration surges dramatically mid-cycle to induce ovulation, as per reproductive endocrinology.

Why the others are wrong:

• A. FSH rises early in follicular phase to stimulate follicle growth, without mid-cycle peak.
• C. Oestrogen increases gradually before ovulation but lacks LH's sharp surge.
• D. Progesterone rises post-ovulation in luteal phase, not mid-cycle.

Final answer: B