How many variables are there in science

i'm hoping this is like a multiple answer question. if it is then it would be, the location of the plants and also the height of the plants since one she wants to know where in her garden the chamomile grows best. but also to see which plants grew better in the location she also has to measure the plant itself. (if you can only choose one answer than it would be c).

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.