Explanation:

To measure small lengths, we use a 15 cm scale. This is the correct option out of the given choices.

Reasoning:

When measuring small lengths, it is important to use a tool that provides accurate measurements and is suitable for the task. The options given, such as a banana, hand, and pen, are not appropriate for measuring small lengths because they do not provide accurate measurements or are not designed for this purpose.

A 15 cm scale, on the other hand, is a tool specifically designed for measuring small lengths. It has markings in centimeters, which allows for precise measurements. The scale is usually made of plastic or metal and has a straight edge for measuring straight lines. It is commonly used in schools, offices, and households for various measurement tasks.

Benefits of using a 15 cm scale:

1. Precision: A 15 cm scale provides accurate measurements in centimeters, allowing for precise calculations and comparisons. This is particularly important when measuring small lengths where even a small error can significantly affect the result.

2. Convenience: The compact size of a 15 cm scale makes it easy to carry and use for various measurement tasks. It can fit in a pencil case or pocket, making it readily accessible whenever needed.

3. Versatility: A 15 cm scale can be used for measuring both straight lines and curved surfaces. The straight edge of the scale can be used to measure the length of objects or draw straight lines, while the curved edge can be used to measure circular or curved objects.

4. Durability: Most 15 cm scales are made of durable materials like plastic or metal, ensuring that they can withstand regular use and remain in good condition for an extended period.

In conclusion, a 15 cm scale is the appropriate tool for measuring small lengths due to its precision, convenience, versatility, and durability. It is widely used in educational, professional, and personal settings for various measurement tasks.