We thank the reviewer for his helpful comments. Yang's research was partly supported by the National Basic Research Program (973 Program) of China (2007CB814905) and the National Natural Science Foundation of China (Grants No. 10871008). Yang also thanks National Science Foundation (DMS-0630950) of the US for supporting his visit to Texas A&M University through the Virtual Center for Collaboration between Statisticians in the US and China, where some initial ideas of the project was developed. Huang's research was partly supported by the National Cancer Institute (CA57030) and the National Science Foundation (DMS-0907170) of the US, and by Award No. KUS-C1-016-04, made by King Abdullah University of Science and Technology (KAUST).