Final answer:
According to Hebrews 11:7, by faith Noah was moved with reverent fear to construct an ark, indicative of the importance of acting by faith despite uncertainty.
Step-by-step explanation:
According to Hebrews 11:7, By faith Noah, being warned by God concerning events as yet unseen, in reverent fear constructed an ark for the saving of his household. Therefore, the answer to the question is a) Fear. Noah acted by faith when he built the ark, even though he had not yet seen the flood that God told him would come. This verse is often cited to demonstrate the importance of faith in action, even under uncertain circumstances.