【单选题】

Which of the following best explains the expression "oil is the albatross of US national security" in Paragraph 5
A．(A) Oil problem poses serious threat and burden to US national security.

B．(B) Securing enough oil supply is the top priority in US national defense policy.
C．(C) Oil symbolizes the current situation of US national security.
D．(D) US national security should focus more on oil.