中国民航行业标准甚高频技术规范中规定甚高频天线的特性阻抗应为()。
A.50
B.75
C.60
D.80
参考答案:A
已知|x-1|+|y-2|+|z-3|=0,则x+2y+3z=( )。
Recently people have made great progress in using ____ power of nature to produce____ electricity.
A.a; the
B./; /
C.the; /
D.a; an