**Core Concept**
Bipolar affective disorder (BPAD) is a mood disorder characterized by recurrent episodes of mania or hypomania, often alternating with depressive episodes. It is a complex condition involving fluctuations in mood, energy, and activity levels.

**Why the Correct Answer is Right**
The correct answer is **c) Depressive episodes and hypomanic episodes**. This is because BPAD is defined by the presence of at least one manic episode, which may alternate with depressive episodes. Hypomanic episodes are a milder form of mania, characterized by elevated mood, reduced need for sleep, and increased energy, but without the severity and impairment seen in manic episodes. The combination of depressive episodes and hypomanic episodes is a hallmark of BPAD.

**Why Each Wrong Option is Incorrect**
* **Option A:** Recurrent depressive episodes are a common feature of BPAD, but they are not the defining characteristic. Depressive episodes can occur in isolation, without the presence of manic or hypomanic episodes.
* **Option B:** Recurrent manic episodes are a key feature of BPAD, but they do not occur in isolation. Manic episodes are often followed by depressive episodes or vice versa.
* **Option D:** Manic episodes and depressive episodes are both features of BPAD, but the combination of depressive episodes and hypomanic episodes is more specific and diagnostic.

**Clinical Pearl / High-Yield Fact**
To remember the defining features of BPAD, use the mnemonic "HYPOMANIA-HYPOMANIA" which stands for "Hypomanic episodes preceding or following depressive episodes".

**Correct Answer:** C. Depressive episodes and hypomanic episodes