题目

In the 1960s, medical researchers Thomas Holmes and Richard Rahe developed a checklist of stressful events. They appreciated the tricky point that any major change can be stressful. Negative events like “serious illness of a family member” were high on the list, but so were some positive life – changing events, like marriage. When you take the Holmes – Rahe test you must remember that the score does not reflect how you deal with stress – it only shows how much you have to deal with. And we now know that the way you handle these events dramatically affects your chances of staying heal如图，在四棱锥P-ABCD中，PD⊥平面ABCD，AB=BC，BD⊥AC，E为PC的中点．（Ⅰ）求证：AC⊥PB；（Ⅱ）求证：PA∥平面BDE．