**Core Concept**
Ethinyl estradiol is a synthetic form of estrogen used in combination with progestins for oral contraceptive pills (OCPs). The dosage of ethinyl estradiol in OCPs has been reduced over the years to minimize side effects while maintaining efficacy.

**Why the Correct Answer is Right**
The content of ethinyl estradiol in very low dose OCPs is typically less than 20 micrograms (mcg). This low dose is designed to reduce the risk of venous thromboembolism and other estrogen-related side effects while still providing effective contraception. The reduction in estrogen dose also leads to a decrease in the risk of breast tenderness, mood changes, and other symptoms associated with estrogen.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the content of ethinyl estradiol in very low dose OCPs is typically less than 20 mcg, not more than 20 mcg.
**Option B:** This option is incorrect because the content of ethinyl estradiol in very low dose OCPs is not equal to 20 mcg; rather, it is less than this amount.
**Option C:** This option is incorrect because the content of ethinyl estradiol in very low dose OCPs is not equal to 40 mcg; rather, it is less than this amount.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the dosage of ethinyl estradiol in OCPs has been reduced over the years to minimize side effects while maintaining efficacy. This reduction in estrogen dose is a key factor in the development of very low dose OCPs, which are designed to provide effective contraception with a lower risk of estrogen-related side effects.

**Correct Answer: D. 10 mcg**