明天就要考了，请教一道新PREP的语法题

if current trends continue, by the year 2010 carbon emissions in the United States will soar to a level more than one-third higher than were those in 1990, according to official projections.

答案是：will soar to a level more than one-third higher than that

说起来有点伤心，明天就要上刑场了，今天还被这样一道题目难为了。我想问，这里的that 是指句子里的a level么？

先谢过各位了

还有一道：Besides adding complementary flavors to many foods, hot sauces stimulate the release of endorphins in the brain, just as exercise does, and these have a pain-relieving effect like morphine's.

这里的these为什么可以做主语呢？

谢谢！