Which is a correct guideline of science? a) hypotheses may or may not be testable b) explanations are based on observations, evidence, and testing c) scientific knowledge does not need peer review and verification before acceptance d) understandings and/or conclusions will never change with additional empirical data

Option A cannot be true since a scientific hypothesis must be testable, otherwise it is not scientific.

Option C is incorrect as well as scientific knowledge DOES need peer review and verification before the results are accepted by the scientific community.

Option D is also false as science is always changing and adapting. What this means is that conclusions or understandings can be changed if new evidence surfaces that suggests otherwise.

Therefore, the only correct answer is B) Explanations are based on observations, evidence, and testing.

This is true as we cannot make statements or explanations in science without first conducting tests, making observations and gathering evidence to support our claims.