A:低碳生活注重节能减排,减少温室气体的排放
B:推广使用可降解塑料及布质购物袋,以减少“白色污染”
C:半导体行业中有一句话:“从沙滩到用户”,计算机芯片的材料是二氧化硅
D:启用大气中细颗粒物(PM2.5)的监测,以追根溯源,采取措施,改善空气质量
A
Today is August 3rd. Tomorrow (明天) is Peter's grandfather's birthday. It is his 73rd birthday. Peter's two sisters, Sally and Tina, and Peter buy some things for their grandfather this afternoon. Sally buys a nice birthday card. And she writes(写) “Happy birthday” on it. Tina buys a blue shirt from a clothes store. It is $29. Peter buys some fruits and a set of books. The name of the books is Harry Potter (哈里波特)
如图所示,小球P连接着轻质弹簧,放在光滑水平面上,弹簧的另一端固定在墙上,O点为它的平衡位置,把P拉到A点,使OA=1cm,轻轻释放,经0.4s小球运动到O点.如果把P拉到A′点,使OA′=2cm,则释放后小球这一次运动到O点所需的时间为( )