When Mr. Valdez thought his - year-old daughter had fallen down the stairs, his heartbeat accelerated, his blood pressure rose, and he began to perspire heavily. Mr. Valdez's state of arousal was activated by his nervous system

Sympathetic Nervous System.

Explanation:

The system which generates fight or flight response is the sympathetic nervous system.

The fight or flight response is the involuntary action of our nervous system. In this, our nervous system is directed unconsciously. In such a situation, our body starts functioning in a certain manner such as changes in heart rate, sweating, digestion, body temperature, etc.

So, in the given situation the state of arousal of Mr Valdez was because of the sympathetic nervous system.