They have studied in this school .
A:since three years ago
B:three years ago
C:for three years ago
D:since three years
大自然的语言丰富多彩:从秋叶的飘零中,我们读出季节的变化;从归雁的行列中,我们读出了集体的力量;____,____。
青蛙、家燕、小麦个体发育的起点都是受精卵。
“看万山红遍,层林尽染,漫江碧透,百舸争流,鹰击长空,鱼翔浅底,万类霜天竟自由”描述了( )