We all know that overseas development assistance allocated to agriculture dropped from 18 percent in 1978 to just over four percent in 2008, The amount of money spent by developing countries on agriculture during that same period also dropped sharply.

VOA: standard.2010.03.29

So, the process of developing a vaccine occurred over a long period of time.

疫苗的发展经历了很长一段时间

耶鲁公开课 - 生物医学工程探索课程节选

So, the process of developing a vaccine occurred over a long period of time.

疫苗的发展经历了很长一段时间

耶鲁公开课 - 生物医学工程探索课程节选