'When American Sneezes, Britain Catches Cold

'When American sneezes, Britain catches cold.' Which of the following does this phrase best highlight?

A) International travel means that viruses can now be spread quickly on a global scale.
B) Medical research now involves collaboration between international teams based in different research centres across the globe.
C) The connected nature of the global economy means that problems in one national economy can have knock on effects globally.
D) Winter is at different times of the year in different parts of the globe.