原来不知道，将来也不一定用得到，不过觉得可能有人用得到，就贴一下好了：
If you plan to visit more than one employer on your trip, pro-rate the
expenses among the employers. If you are visiting two or more employers on
the trip and only one employer is willing to pay expenses, the employer
should be charged only the share of the cost in proportion to the number of
employers visited. http://www.d.umn.edu/careers/cs_handbook/cshandbook_types.html
