What part of a drill allows for easy bit changes?

The chuck is the part of a drill that is specifically designed to hold the drill bit in place and facilitate easy changes of the bit. It can be either a keyed or keyless type.

In a keyless chuck, for example, you can simply grip the chuck and twist to tighten or loosen it, allowing you to change bits quickly without needing additional tools. This feature is especially useful in situations where time is critical or when you're switching between different types of drilling tasks that require different bits.

The base and handle are components that contribute to the overall usability and ergonomics of the drill but do not directly affect the process of changing bits. The battery pack provides power to the drill but is unrelated to how bits are secured or released from the tool. Hence, the chuck is the correct answer as it is specifically designed for this purpose.