In which of the following countries, does only one standard time exist?

• Mexico

• Sri Lanka

• New Zealand

• China

From the following countries China is the country which has only one standard time zone which is followed by easternmost China and westernmost China. This was the Communist Party decision to use Beijing time across the country to enhance national unity. From most people in China, the single time zone is at most mild inconvenience a scheduling quirk that simply requires a little adjustment.