Question

Not all amino acids have to be supplied by food. this is true because:

Answer 1

"b. the liver is able to manufacture some amino acids from others."

The liver has the capability to transform some amino acids into others (called non-essential because they can be produced by the body and there is no need to get them from food). This is done by transamination. Transamination is the process of transferring an amino group from one molecule to another without forming ammonia thanks to enzymes that are called transaminases and preform such transfer.