Please help me asap ill mark you as brainiest

Probably A

the biosphere is mostly not blue and D just isn't relevant to that question

The hydrosphere looks blue and covers three-fourths of the Earth's surface.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.