问题如下：
Which statement is most accurate? A common size income statement:
选项：
A. restates each line item of the income statement as a percentage of net income.
B. allows an analyst to conduct cross-sectional analysis by removing the effect of company size.
C. standardizes each line item of the income statement but fails to help an analyst identify differences in companies’ strategies.
解释：
B is correct.
Common size income statements facilitate comparison across time periods (time-series analysis) and across companies (cross-sectional analysis) by stating each line item of the income statement as a percentage of revenue. The relative performance of different companies can be more easily assessed because scaling the numbers removes the effect of size. A common size income statement states each line item on the income statement as a percentage of revenue. The standardization of each line item makes a common size income statement useful for identifying differences in companies’ strategies.
公司规模是不同的（比如市值不同），收入费用的绝对金额是跟规模挂钩的，单独的比较不同公司的NI其实并没有可比性，而common-sized I/S是把I/S中的各项都除以了revenue，这样就剔除了规模的影响，可以用各项占比来进行比较，选项A错误，选项B正确。
分析师可以分析不同公司费用都花到了什么方向，以此来比较各公司的战略，比如有的在R&D上花的钱多，有的在广告方面花钱多，这代表了两种不同的发展战略，可以通过相关费用占比来进行分析。选项C错误。
怎么理解这部分题里的横向cross和纵向vertical，这个是哪个知识点
