The word "concrete" in the second sentence of the passage means

A．Science answers questions about accurate facts.
B．Science answers questions about observations.
C．Scientists cannot study the social consequences of beliefs.
D．Scientists can study the truth or error of beliefs.

A．scientific knowledge is based on verifiable evidence.
B．science does not have answers for verifiable evidence.
C．science has no absolute truths.
D．the scientific method requires that all conclusions be open to reexamination whenever new evidence is found to challenge them.