若$\frac{x-2y}{3y-x}$=$\frac{2}{3}$，则$\frac{y}{x}$为（　　）

显微镜能帮助我们观察到用肉眼无法看到的细微结构，如图分别为镜头、显微镜和在显微镜下看到的细胞图象，请据图回答：

 ①1866年孟德尔的豌豆杂交实验，提出遗传定律

 ②1910年摩尔根进行果蝇杂交实验，证明基因位于染色体上

 ③1903年萨顿研究蝗虫的减数分裂，提出假说“基因在染色体上”

    What will our world be like in 2050? A group of experts has made____(they) predictions about our life.

    It is____(believe) that we will have “clever”cars by 2050. We won't have so many accidents b____they will probably be able to communicate with each other. Cars will slow down by themselves or stop in____(danger) situations.

    What's more we will never d____! Our brains will be put onto computers and we can live forever. The computers of____future won't look like machine. They'll look like____

    By 2050 there will be less____ (pollute). The factories will be ____(build)on the moon and other planets. We will be able to spend holidays on Mars and be back ____ spaceship in just a few days.