锯削运动一般采用______运动,速度一般为______左右,锯削硬材料______些,锯削软材料______些。
参考答案:小幅度上下摆动式;40次/分钟;慢;快
Population experts say that by 2050 the world will have about 2 billion people aged over 60,____as today.
A.as three times
B. three times as many
C. three times many
D. three times many as
世界卫生组织1946年给健康下定义的认为,健康是指();();()的完善状态,而不仅只是没有疾病和衰弱的现象。