What does it mean to be a sad ?

Explanation:

To enter a stage of negativness

I'm trying to reach a new rank so I'd appreciate you marking me as brainliest. If you don't want to it's okay, have a nice day.

See below:

Explanation:

Although this is a very varying question, scientifically, being sad is when a hormone called serotonin is altered. Being sad is not a good feeling. It is a feeling of being low, not in the mood for laughter and joy, and overall being irritable and unhappy. Often times people are sad for reasons that cause sadness, like the loss of a loved one or an argument with a friend.

the answer is; comparing the frequency of collisions with and without the device

this makes the anti-collision system an independent variable and the collisions a dependent variable. if there are fewer collisions with an anti-collision system that without, then it can be stated that the system is a success. essentially, collisions under an anti-collision system are compared with the frequency of collisions by cars with the human drivers.

cuz he is really really short, assuming an unorthodox and inherently unlucky configuration of elevator buttons…

explanation: