A:元杂剧
B:昆曲
C:明传奇
D:京剧
They found _______ difficult to communicate with people from different countries.
图钉帽的面积是0.8平方厘米,图钉尖的面积是0.0005平方厘米,手指对钉帽的压力是20N,手对图钉帽的压强是 ____ Pa.图钉尖对墙的压强是 ____ Pa.