The number of people in the world__________ about 6 billion and large quantities of waste ____ each year.

A．total; has been produced

B．totals; is produced

C．totals; are produced

D．total; are being produced

热退火酸洗线退火炉冷却分为三部分，分别为空气冷却、（）冷却、喷水冷却。