来自不同光源的两束白光,例如两束手电筒光,射在同一区域内,是不能产生干涉花样的,这是由于( )
A. 白光是由许多不同波长的光构成的
B. 不同波长的光速是不相同的
C. 两光源发出不同强度的光
D. 两个光源是独立的,不是相干光源
Yu Lili wants to sign up for a volunteer organization. She is talking with Chen Fei about it. Listen to their conversation and fill in the blanks with the choices marked A to G.The Benefits Volunteering Work will Do for Yu Lili(1) ___________________________________;(2) ___________________________________;(3) ___________________________________.
A. no need to spend much time on her studies
B. improve her ability to communicate with people
C. leave campus to do volunteering work
D. help her get teamwork experience
E. help those people in need
F. add something to a nice-looking résumé
G. get some relaxation on Saturdays and Sundays
为使回归方程的精度提高,在选择因子时,要使因子之间相关系数尽可能( ),各自与预报量的相关系数尽可能( )。
A. 大,大
B. 大,小
C. 小,小
D. 小,大
求回归系数的方法是()。
A. 傅里叶变换法
B. 费史判别准则
C. 最小二乘法
D. 谱方法