Real all pages in file1
This means that we are accessing all the records under all the pages$\left (P_{1}, P_{2}, P_{3},......, P_{1000} \right )$ under FILE1. For locking records protocol first need to lock the ancestors in IS mode. Protocol will lock D in IS mode then F1 in IS mode then it will finally lock $\left (P_{1}, P_{2}, P_{3},......, P_{1000} \right )$ in IS and shared lock to the records.
Hence option A is correct.