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

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.

A．evidence is basically a value judgment.
B．evidence is basically an esthetic judgment.
C．evidence is basically a purposeful judgment.
D．evidence is basically a factual judgment.