改成:奉茶期间,主人要仔细观察客人茶杯里的茶量。While severing tea ,the host should pay close attention to the guests’ cups, refilling as frequently as necessary.
个人觉得观察可能用observe好一点,然后茶杯里的茶量可以用其他短语代替比如“The remaining tea in the cup”如果有说错请指出,见谅