A:爱国
B:友善
C:文明
D:敬业
In some cities, the junior pupils look forward to having ______ time to relax and ______ homework to do.
栖树一群鸦,鸦数不知数,三只栖一树,五只没去处,五只栖一树,闲了一棵树.请你仔细数,鸦树各几何?在这一问题中,若设树有x棵,通过分析题意,鸦的只数不变,则可列方程:____.