Answer: The answer is indeed A.Bicyclists who opt not to wear helmets are abandoning good sense and putting their lives at risk.
Step-by-step explanation:
Sentences B, C, and D are objective in the sense that they express facts instead of the speaker's opinion. Helmets are important for safety, they have become more advanced and they protect the brain.
Sentence A, on the other hand, expresses an opinion. The speaker thinks it's lack of good sense not to wear a helmet while riding. Someone else might have a different point of view.