Because it controls the pituitary gland, the brain's ultimately controls the endocrine system.

Because it , the brain's HYPOTHALAMUS ultimately controls the endocrine system.
The hypothalamus is the part of the brain that controls the endocrine system, it does this by linking up the nervous and the endocrine system via the pituitary gland. Hypothalamus functions by releasing hormones which either inhibit or stimulate production of hormones in the anterior pituitray gland.

I’m going to go with b!