题目

Once upon a time, there was a woman baking bread for members of her family and an extra one for a hungry passer-by. She always kept the extra bread on the window-sill, for whoever would   41   it away. Everyday, an old man   42   and took away the bread without   43   gratitude. This went on, day after day, and the woman felt very   44   . In order to punish him, she decided to add   45   to the bread she   46   for him! As she was about to   47  it on the window-sill, her hands trembled. Immediately she threw the bread   48   the fire, prepared another 方程4x2-9=0的解为（ ）A．x=B．x=C．x=±D．x=±