the last half of the nineteenth century ____ the improvement in the means of travela.has witnessedb.witnessed为什么选b不选a 为什么不可以用现在完成时

谁能帮我解释The last half 渚媡he last half of the nineteenth ce帽tury 翻译 the last half of nineteenth century wintnessed the steay improvement in the means of travel half of the Half of the apples (is )bad .（Are )there any people in the room last night? by the end of last month ,they had finished half of their work 是什么时态 the other half of me the half of my life Half of the apples ____good. half the class 与half of the class的区别 half the sky half of the sky区别 half the books还是half of the books? Half of the time to pursue the last of the last of the the last of Last Mile of the Half of the work in our office ____by the computer last year 用was done 还是were done In britain and japan inflation is running half a percentage below the rate predicted at the end of last