题目

阅读理解 Animportant drug that serves as the backbone of treatment for most childhoodcancers, has become increasingly rare, and doctors are warning that they maysoon be forced to consider rationing doses(定量供应剂量)． Therehave been long­term shortages of certain drugs andmedical supplies in the United States for years, but doctors say the loss ofthis medication, vincristine(长春新碱) is leading to lotsof problems, as there is no appropriate substitute. This is truly a sadsituation, said Dr. Yoram Unguru, a doctor at the Herman and WalterSamuelson Children's Hospital at Sinai6．如图，C是∠AOB内部一点，D是∠AOB外部一点，在内部求作一点P，使PC=PD，并且使P点到∠AOB两边距离相等（保留作图痕迹）．