How does caffeine's structural similarity to adenosine allow it to act as an antagonist?

• A. It binds to the adenosine receptor and triggers the normal effect.
• B. It binds to the adenosine receptor, blocking adenosine and preventing its normal effect.
• C. It degrades adenosine before it can bind to its receptor.
• D. It enhances adenosine's binding to its receptor.

Answer: (B)