—Sixteen-year-olds should not be allowed to drive.

—______. It's dangerous. [ ]

A. I don't think so

B. I don't know

C. I disagree

D. I agree

给自行车打气时，越打车胎越硬；放在烈日下的自行车，车轮可能会爆胎，请对上述现象中的原因及结果进行分析，提出一个你认为需要研究的问题：______．