**Core Concept**
Formal thought disorders refer to an abnormality in the way thoughts are organized, structured, and expressed. This can include problems with the flow of thoughts, the connection between thoughts, and the overall coherence of thought processes. **Thought disorders** are a key feature of various psychiatric conditions.

**Why the Correct Answer is Right**
The correct answer includes **circumstantiality** and **loosening of association**, which are both formal thought disorders. **Circumstantiality** involves a circuitous and indirect way of expressing thoughts, where the individual eventually reaches the point but with excessive and unnecessary detail. **Loosening of association** refers to a disorganized thinking pattern where thoughts seem unrelated or loosely connected, making it difficult to follow the individual's train of thought.

**Why Each Wrong Option is Incorrect**
**Option A:** Thought broadcast is a type of **passivity phenomenon**, where an individual believes their thoughts are being broadcast or transmitted to others, which is a delusional perception rather than a formal thought disorder.
**Option D:** Delusion is a firmly held belief that is not grounded in reality, which is a **content-related thought disorder** rather than a formal thought disorder.

**Clinical Pearl / High-Yield Fact**
Formal thought disorders are crucial to identify in psychiatric evaluations as they can significantly impact an individual's ability to communicate effectively and can be indicative of underlying psychiatric conditions such as schizophrenia.

**Correct Answer: C. c) Loosening of association, b) Circumstantiality**