**Core Concept**
The ovulatory phase is a crucial stage in the menstrual cycle where the dominant follicle ruptures, releasing an ovum (egg) from the ovary into the fallopian tube. This phase is characterized by a surge in luteinizing hormone (LH) levels, which triggers ovulation.

**Why the Correct Answer is Right**
The correct answer is related to the hormonal changes that occur during the ovulatory phase. The surge in LH levels stimulates the dominant follicle to release the ovum. This is a critical event in the menstrual cycle, allowing for fertilization to occur. The increased LH levels also trigger the formation of the corpus luteum, which produces progesterone to prepare the uterus for a potential pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not related to the ovulatory phase. The follicular phase is the stage before ovulation, where the follicle grows and matures under the influence of follicle-stimulating hormone (FSH).

**Option B:** This option is incorrect because it is related to the luteal phase, which occurs after ovulation. During this phase, the corpus luteum produces progesterone to support a potential pregnancy.

**Option C:** This option is incorrect because it is a general term that can refer to any stage of the menstrual cycle. It is not specific to the ovulatory phase.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the LH surge is a critical event that triggers ovulation. This surge can be detected in blood or urine tests to determine ovulation and predict fertility.

**Correct Answer: D. Estrogen levels.**