题干
The children are having fun _________ on the beach（海滩）.
A：play
B：plays
C：played
D：playing
答案(点此获取答案解析）
D
The children are having fun _________ on the beach（海滩）.
A：play
B：plays
C：played
D：playing
的分子和分母的最大公因数是
想。从哲学上看，这一标志的出现说明（ ）