27．—There aren't any toys in our suitcase．Where have you put

27．—There aren't any toys in our suitcase．Where have you put them?—Oh,no．That old lady sitti
27．—There aren't any toys in our suitcase．Where have you put them?
—Oh,no．That old lady sitting next to us ______ have taken ours by mistake.
A．must B．could C．should D．would
为什么选A呢?
又为什么不选C呢？