银河系的直径约10²¹m，可用长度单位______来量度，一光年的长度等于以光速走一年时间通过的路程，所以1光年约等于______m；质量的国际制主单位是______．25g（克）=______kg（千克）

Studies show that the things that contribute most to a sense of happiness cannot be bought,

________ a good family life, friendship and work satisfaction.[      ]

A. as for  

B. in view of

C. in case of  

D. such as