Answer:

Safety pins are commonly used for fastening or holding together two pieces of fabric or other materials. They are designed to be secure and easy to use. While safety pins can be made from various materials, the most commonly used pair for making safety pins is steel and plastic.

Steel:
- Steel is a strong and durable material that is commonly used in the production of safety pins.
- It provides the necessary strength and rigidity to the pin, allowing it to hold fabrics and materials firmly.
- Steel also has a smooth surface, which prevents the pin from snagging or damaging the fabric.

Plastic:
- Plastic is used in the production of safety pins for the head or cap of the pin.
- The plastic head makes it easier to hold and manipulate the pin, providing a comfortable grip.
- Plastic is lightweight and does not add unnecessary weight to the pin, making it easy to use.

Advantages of using steel and plastic:
- Steel and plastic combination is ideal for safety pins due to the strength and durability of steel combined with the lightweight and easy handling of plastic.
- Steel provides the necessary strength to hold fabrics together securely, while plastic adds convenience and comfort during use.
- The combination of steel and plastic ensures that the safety pin is strong, reliable, and easy to use.

Other options:
a) Wood and glass: Wood and glass are not commonly used materials for making safety pins. Wood is not strong enough to hold fabrics securely, and glass is fragile and can break easily.
c) Leather and plastic: Leather is not commonly used for making safety pins, as it is not as strong or durable as steel. Plastic may be used for the head or cap of the pin.
d) Plastic and glass: Glass is not commonly used for making safety pins due to its fragility. Plastic may be used for the head or cap of the pin.

In conclusion, the commonly used pair for making safety pins is steel and plastic. Steel provides strength and durability, while plastic adds convenience and ease of use.