Why do sheep need grass to survive

Cause they need it for food

SHEEP ARE HERBIVORES THEY DO NOT EAT MEAT SO THEY EAT GRASS

Explanation:

The different school faucets (frequently and infrequently used) are the manipulated or independent variable. The exact school faucet being tested is chosen (in a sense, manipulated) to test a particular effect or in this case, the presence of more chemical impurities.