What structure is attached to the uterus and provides the fetus with oxygen and nutrients?

The placenta is the correct answer because it plays a crucial role in pregnancy, acting as the interface between the mother and the developing fetus. It is a temporary organ that forms during pregnancy and is attached to the uterine wall. Its primary function is to facilitate the exchange of nutrients, gases, and waste products between the mother and the fetus. Through a network of blood vessels, the placenta allows oxygen and nutrients from the mother's bloodstream to reach the fetus, while simultaneously removing carbon dioxide and other waste products from the fetal circulation.

The other options relate to structures involved in reproduction and pregnancy but do not serve the same purpose. The ovary is responsible for producing eggs and hormones but does not provide direct support to a developing fetus. The womb, commonly referred to as the uterus, is where the fetus develops, but it does not directly supply oxygen and nutrients. The embryo represents the early stage of fetal development but relies on the placenta for essential resources as it grows. Thus, the placenta's unique function makes it the correct answer to the question regarding the structure that provides oxygen and nutrients to the fetus.