问题如下：
DK, a magazine company, received $1,000 subscription fee on 1 January, 2017. Assume it distributes magazines each month, the transaction at the beginning of this year would most likely result in:
选项：
A.no effects on total assets.
B.an increase in revenue of $1,000.
C.an increase in both assets and liabilities of $1,000.
解释：
C is correct. $1,000 subscription fee is unearned revenue. It will not be recognized as revenue, but as a liability. The cash payment will increase the assets. Therefore, both assets and liabilities will increase $1,000.
老师，这个是订阅费是预付款属于unearned revenue，为什么both increase in asset & liability？按照讲义视频里的划分，这笔钱不就应该属于liability吗？我能理解资产负债表为了两边平衡同时相加互相抵消，只是不理解讲义说的liability的性质，怎么理解？有点搞在一起
