Need Help! Jenny is running for more than an hour on a pleasant sunny morning. Her body is sweating to maintain homeostasis, which is caused by the action of a/an _ control center

effector

sensor

transmitter

The sweat that Jenny produces while she is running —to maintain homeostasis— is caused by the action of a control center.

Explanation:

During prolonged physical exercise there is a rise in body temperature, which is the stimulus that activates the sweating process.

The sweat control center is located in the pre-optic area, just in front of the hypothalamus, and is in charge of sending the signal to the sweat glands to produce sweat.  Sweating is one of the mechanisms used to regulate body temperature —homeostasis— when it increases due to physical exercise.

As for the other options:

    Efector, sensor and transmitter are elements that participate in the physiological response to stimuli, together with the control or regulation centers of the nervous system.