'Metal dishes'' (Dish Antennas) are used for receiving TV signals from distant communication satellites. These 'Metal Dishes' are :

Options

A. Convex reflectors
B. both convex and concave reflectors
C. Concave reflector
D. Convex refractors

Explanation

To solve the question regarding the type of reflector used in metal dishes (dish antennas) for receiving TV signals from distant communication satellites, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Purpose of Dish Antennas**:
- Dish antennas are designed to receive signals from satellites. Their shape plays a crucial role in how effectively they can gather and focus these signals.

2. **Identifying the Shape of the Dish**:
- The shape of the dish is critical. To effectively collect signals, the dish must be able to focus incoming signals onto a specific point.

3. **Analyzing the Reflector Type**:
- The type of reflector that can concentrate signals at a single point is a concave reflector. This is because a concave shape allows parallel rays (like those from a satellite) to converge at a focal point.

4. **Conclusion**:
- Since the dish antenna is designed to focus signals onto a receiver, it must be a concave reflector. Therefore, the answer is that the metal dishes (dish antennas) are concave reflectors.

### Final Answer:
The metal dishes (dish antennas) used for receiving TV signals from distant communication satellites are **concave reflectors**.

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