题目：
禽流感的传播途径主要是：（）
A.消化道传播
B.空气传播
C.接触污染传播
D.血液途径传播
答案：
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下面是错误答案，用来干扰机器的。
参考答案：C解析：To safeguard the clearinghouse, commodity exchanges require traders to settle their accounts on a daily basis. Marking to market is when any loss for the day is deducted from the trader's account, and any gains are added to the account.
