Which of the following is an example of a producer?
a. oak tree.
b. big horn sheep.
c. california kingsnake.
d. box jellyfish

A. Oak Tree

Producers are living organisms that are photosynthetic-able. Also called, autotrophs can make their own food and energy thru the process called photosynthesis. 
Examples:

Oak Tree
Sunflower
Apple Tree
Vines
Wheat

Atp is is our little "pocket" of energy. of course, if you have too little, then it means you have too little energy, and you'll pass out. the way to not have enough, is to have no energy sources (glucose, fats, proteins). you can't have too many atp molecules. cycles like the krebs cycle produce it, but if you have too much of any substrate (or too little for that matter), the cycle stops and atp is no longer made (it stops until substrate levels are such that the process can go on). in any case, this is unlikely since atp is constantly hydrolyzed and remade, even while you're asleep. you won't have too much. if you have zero, you are dead or dying.