Kentucky Fried Chicken has 1,100 outlets in China, about ____ those of McDonald’s.
A as many as twice B as twice as many
C many as twice as D twice as many as
想请益一下这题文法，个人是选择A，答案是D，有点疑惑><上来发问
Because of the advanced medical technology, infant mortality ______ in the past
thirty years.
A has fallen B had fallen C is falling D was falling
个人是选择B，答案是A，句意中不是past thirty years? 可以用现在完成式?
以上两题问题，感谢帮忙Thanks!!

1.应该算是固定用法吧 twice/two times等都是这样用twice as much/two times as many...2.past thirty years期间一直都在降 没有明确的过去时间点,会用现在完成式

2. "has fallen"过去三十年间直到现在都还在减少如果用"had fallen"，那是说曾经减少过，但是后来又回升了

"the past thirty years"意思是从“现在”算起的过去30年间。在时间区间的涵盖范围上包含“现在”，所以可以用现在完成式http://www.ldoceonline.com/dictionary/past_1-> 2 .... (注意读字义说明和例句)context合适的话是有可以使用 过去完成式 的情况，只是像这种没有额外context的单一句子一般不使用过去完成式(因为没有一个"较近"的过去时间（事件）当参考点)比如: http://ppt.cc/vV9X (此处的"in the past century"是指以那manuscript作者写作的“过去”时间当起点(当参考点)--那之前的一百年，所以大约是 175x 到 185x这内容就只是（引述）那manuscript所讲的“过去”情况，和“那之后(185x -- 2014现在)的情况”无关