A:地月系
B:太阳系
C:银河系
D:河外星系
— Your painting really improves a lot.
— I have taken a painting ________ since last year. I find my painting is getting better.
计算下列各题能简算的要简算
①( 115 + 217 )×15×17
②2011× 20092010
③777×9+37×111.