Before revision:  In this paper, we aim at better algorithms under the assumption that all the requests with the same booking time arrive simultaneously. Indeed, we propose a randomized algorithm which can achieve a competitive ratio of \frac{4{k + \lfloor k/3 \rfloor} for all k\geq 2.
After revision:  In this paper, we remove all the holes of unknown CR; namely we prove that the CR is \frac{2k{k + \lfloor k/3 \rfloor} for all k\geq 2.