【名词&注释】
核黄素(riboflavin)、信用证结算(letter of credit settlement)、银行汇票(bank draft)、安全地(be safely)
[单选题]An isotherm is().
A. a line on a weather map connecting equal points of both temperature and pressure
B. an instrument that measures the climatological effects of temperature
C. a line connecting points of equal barometric pressure on a weather map
D. a line connecting points of equal temperature on a weather ma