Models are simplified representations of of different complex systems. They also help to study very small or large objects.
Option B, D and E.
Explanation:
Models are very simplified representations of complex systems and organs or structures which are prepared to study those systems by scientists and normal people easily. Many structures of human body like cells or some tissues are very small in structure or microscopic in nature. So studying them are very hard without specific instruments which are not always available. Thus models are made to easily study those structures by scientists and even normal people and students.
I believe D because if the fertilizer had a concentrated source of nitrate (which plants do need) then when watering that can go into the ground water which is underground <span />
5% of $20 is $1; 5% off $20 is $19
