看图,根据字母提示,重新组合单词,并写在四线三格中。
e n t e e g h i
____
(Ⅰ)证明:PA⊥BD;
(Ⅱ)若PD=AD,求二面角A﹣PB﹣C的余弦值.
The house price is going up _______.
方程组3x-4y=1x-4y=7的解是____
A. Father's Day
B. Children's Day
C. summer vacation
D. China's National Day