单项选择题A．the demand is too lowB．the supply is too largeC．the cost is too highD．the price is changeable

单项选择题A．nearest of all planets to the sunB．extremely hotC．little known to peopleD．biggest of all planets

单项选择题These references most probably appear ______.

单项选择题The terrible pain during a crisis is caused by______.

单项选择题According to the passage, which is NOT TRUE of sickle-cell anemia