**Core Concept**
Diethylstilbestrol (DES) is a synthetic estrogen that was prescribed to pregnant women in the 1940s-1960s to prevent complications of pregnancy, such as miscarriage and premature labor. However, it has been linked to various health problems in the offspring of these women, including an increased risk of certain cancers.

**Why the Correct Answer is Right**
The increased risk of cancer in the offspring of women who took DES during pregnancy is thought to be due to the exposure of the developing fetus to this synthetic estrogen. This exposure can disrupt normal fetal development, leading to changes in the reproductive system and an increased risk of cancer later in life. The most commonly affected cancers are clear cell adenocarcinoma of the vagina and cervix, which are both types of cancer that are associated with estrogen exposure.

**Why Each Wrong Option is Incorrect**
**Option A:** Clear cell adenocarcinoma of the vagina and cervix are the most commonly associated cancers, but not the only ones. Other cancers, such as ovarian cancer, have also been linked to DES exposure.

**Clinical Pearl / High-Yield Fact**
The DES story highlights the importance of careful evaluation of the safety and efficacy of medications during pregnancy and the need for long-term follow-up studies to identify potential health risks.

**Correct Answer:** C. Clear cell adenocarcinoma of the vagina and cervix.