Assertion (A): Shark belongs to cartilaginous fishes.
Reason (R): Gill slits are not covered by opericulum.

Options

A. Both A and R are true and R is the correct explanation for A.
B. Both A and R are true but R is not the correct explanation for A.
C. A is true and R is false.
D. A is false and R is true.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Shark belongs to cartilaginous fishes."
- Sharks are indeed classified under the class Chondrichthyes, which are known as cartilaginous fishes. This classification is based on their skeletal structure, which is primarily made of cartilage rather than bone.

2. **Understanding the Reason**: The reason given is "Gill slits are not covered by operculum."
- In cartilaginous fishes, such as sharks, the gill slits are exposed and not covered by a bony structure called the operculum, which is found in bony fishes (Osteichthyes). This is a characteristic feature of cartilaginous fishes.

...