A：盐水
B：自来水
C：蒸馏水
D：矿泉水
在如图所示的光路图中，分别填入合适的透镜和能矫正该眼睛视力的透镜．
如果关于x的方程x2-ax+a-1=0有两个相等的实数根，那么a的值等于____.
relaxing, on, hour, useful, an, and, finish, from, favorite, after
Dear Jack,
I am very busy____Friday. At 8:00 I have math. It is not fun. The teacher says it is____ but I think it is difficult.____ that, I have P.E. at 11:00. It is easy____fun. Lunch is____12:00 to 1:00. I have Chinese at 1:20. It is my____subject. My classes____at 2:00, but then I have____art lesson for two____. It is really____.
How about you?
Yours,
Lucy
如图：在四棱锥P﹣ABCD中，底面ABCD是菱形，∠ABC=60°，PA⊥平面ABCD，点M，N分别为BC，PA的中点，且PA=AB=2．
（Ⅰ）证明：BC⊥平面AMN；
（Ⅱ）求三棱锥N﹣AMC的体积；
（Ⅲ）在线段PD上是否存在一点E，使得NM∥平面ACE；若存在，求出PE的长；若不存在，说明理由．
