D

问题如下：

Which of the following statements about the externalities and their impact on cybersecurity is correct?

选项：

A.

System-wide cybersecurity investment depends solely on the efforts of the strongest member.

B.

Public opinion has no impact on systemic risks during cyber attacks.

C.

Reliance on a few cloud service providers does not introduce concentration risks.

D.

System-wide cybersecurity is a public good, with security levels depending on the weakest member's effort.

解释：

A is incorrect. The level of cybersecurity within a system actually depends on the effort of the weakest member, not the strongest.

B is incorrect. Public opinion can exacerbate systemic risks during cyber attacks, not have no impact.

C is incorrect. Reliance on a few cloud service providers introduces concentration risks, increasing systemic risk.