Amino acids are the building block of protein !!!
Starch is a high molecular weight substance; therefore, it is insoluble to our cells. It needs to be broken down to simple sugars like glucose in order for it to be dissolved/absorbed in our blood. This is because simple sugars has smaller molecular weights and are more soluble.
D is the answer because carbondioxide and oxygen are both needed for plants or green plants to survive.
I hope it helped
