In the beginning, there is a pair of positive integers (m,n) written on the board. Alice and Bob are playing a turn-based game with the following move. At each turn, a player erases one of the numbers written on the board, and writes a different positive number not less than the half of the erased one. If a player cannot write a new number at some turn, he/she loses the game. For how many starting pairs (m,n) from the pairs (7,79), (17,71), (10,101), (21,251), (50,405), can Alice guarantee to win when she makes the first move?<spanclass=′latex−bold′>(A)</span>4<spanclass=′latex−bold′>(B)</span>3<spanclass=′latex−bold′>(C)</span>2<spanclass=′latex−bold′>(D)</span>1<spanclass=′latex−bold′>(E)</span>None of above