What Is the Difference Between Informal Versus Formal Assessment

What is the difference between informal versus formal assessment?

A) Formal assessment is used in research to measure an effect, whereas informal assessment is used in daily clinical work to observe client functioning or changes in the therapeutic relationship.
B) Formal and informal assessments are used in research to increase the validity and reliability of an art therapy program.
C) Formal assessment is used by psychologists in standardized tests; art therapists use informal assessment because art is not proven to be valid.
D) Formal assessment is used in art therapy when the therapist names and publishes an evaluation procedure; informal assessment may be in development but has not been published.