在全民族树立艰苦奋斗精神是实现现代化的重要保证。下列能体现这一精神的是 （ ）
A：少壮不努力，老大徒伤悲
B：桃李潭水深千尺，不及汪伦送我情
C：红军不怕远征难，万水千山只等闲
D：欲穷千里目，更上一层楼
In April, the weather in some places in Shanxi was really changeable. People still remember they have _______ four seasons in a week.
袋中有4个红球，x个黄球，从中任摸一个恰为黄球的概率为34，则x的值为____
Our country is taking action to air pollution.
