C. is the answer because there us mutualism between both species.
Density is mass of object per unit volume
Water. Glucose { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } and Oxygen { O }_{ 2 } gets in, Carbon dioxide { CO }_{ 2 } and water { H }_{ 2 }O comes out from the reaction.
{ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }(s)+6{ O }_{ 2 }(g)\rightarrow 6C{ O }_{ 2 }(g)+6{ H }_{ 2 }O(l)+heat is the exact reaction.
They are different in structure as one serves in an open system (lymphatic system) while the other serves is closed system (circulatory system).
Hope this helps!
*This question is common, so this answer I use a lot. I copied my own work.*
