6、切,则动圆心的轨迹是()A抛物线 B圆 C双曲线的一支 D椭圆13..把一条长 10 厘米的线段随机地分成三段(提问者注:三段不一定是整数),这三段能够构成三角形的概率是( ) A.1/3 B.1/4C. 3/10 D.3/514.Many farmers have adjusted to changing economic fortunes by taking a second job rather th
7、an leave farms ____.A ahead B always C altogether D already15.We___the story at the point where John has lost his job at the newspaper office.A fill out B put down C give away D pick up16.There are three bas
8、ic ways of _____ language to writing, and all known graphic s