The hypothalamus, thalamus, and cerebrum are all parts of which brain region?

The forebrain is the largest and most complex part of the brain, and it is responsible for a wide range of functions, including complex cognitive functions such as thinking, reasoning, and memory. It is divided into two main parts: the cerebrum and the diencephalon.

The diencephalon contains several important structures, including the thalamus, hypothalamus, and pituitary gland.

Hence, the correct option is forebrain.