What is the most common known biological cause of intellectual disability?

Siblings, Rafael and Marina both graduate from a very exclusive college prep high school. Marina continues her education at an Ivy League University and becomes financially successful while Rafael barely meets the graduation requirements at the local community college and never is successful enough to develop a career that financially supports him. Differences in their intellectual growth has also been influenced by:

A. personal characteristics that affected how they took advantage of their opportunities B. the differences in their genetic endowment C. the environment they were raised in D. the different sizes of their brains

Joshua is experiencing a manic episode, but he has a wide variety of symptoms. Although he sometimes feels very good about himself and "high on the world," he sometimes feels sad and anxious at the same time. He finds it hard to explain to his therapist how he can feel both good and bad at the same time. Joshua is experiencing a manic episode with ________ features.

a. dysphoric b. mixed c. euphoric d. psychotic