A bird lear to sing and to fly rapidly at the right time, but the proce is slow and hard once the critical stage has pa ed.

• 一只小鸟能在适当时机较快地学会鸣叫和飞翔，可是一旦关键阶段过去，学会鸣叫和?飞翔的过程就会缓慢而艰难。