Which triangle is similar to △BCD?
Please help me is it A, B, or C please help me please

How do you determine whether a relationship represented as as graph is linear or nonlinear

Having a hard time understanding this question (see attachment).

Aclassmate thinks that solving a system by graphing gives an exact answer when the lines appear to cross at a grid point, but only an approximate answer when they don't. explain why this isn't true.