what is desf and dumb,but can always tell the truth?

what is desf and dumb,but can always tell the truth? 1.What changes a pear into a pearl?2.What has a neck but no throat?3.Two persons are standing on a hill,and one is father of the other's son.What relation are the two each other?4.Which letter is most useful to a desf woman? What is five and five? what is five and two? What is five and tow? What is five and three? what is one and one? what is twelve and fourteen What is one and one? What is nine and thirteen what is relationship she and What is eleven and thiry? and what is your name? what is forever and ever what is capital and reserves? What is Trick and Treat? What is Houyhnhnms and yahoos? what is 6and 这里的and