单项选择题
One of the obligations a bank has to a customer （）
A．is that it can’t take instructions from other people B．is that it can avoid complications and problems C．it must pay money to the customer even if he is seriously overdrawn D．it must print the customer’s signature
单项选择题 The author states that birds left the tropics because （）
单项选择题 The main topic of the passage is （）
单项选择题 A suitable title for this passage might be （）
