What can we infer from the passage?

A．The surface of cold viruses looks quite similar.

B．Scientists have already found a cure for the common cold.

C．Scientists were not aware of the existence of rhinovirus C until recently.

D．Knowing the structure of cold viruses is the key to developing an effective cure.

析：D　考查推理判断。根据第三段最后一句“To do that, the drug must fit and lock into the virus like the right piece of a jigsaw (拼图), which means scientists have to identity the virus and build a 3D model to study its surface before they can design an antiviral drug that is effective enough”，并结合对本段的整体理解可推知，了解感冒病毒的结构是研发有效药物的关键所在，故选D项。