Indeed,volatile food prices, population growth, low agricultural productivity and the potentially devastating effects of climate change make it a particularly daunting challenge. The IFAD president says over the past 30 years, agricultural productivity in developing countries has been stagnant or in decline. He blames it on years of under-investment.

VOA: standard.2010.03.29

So literary can sometimes be very abstract like mathematics, and therefore, if someone says make me a movie, showing me what the square of minus two means that is going to be a challenge.

文学有时候也可以很抽象,像数学，因此如果有人说,给我做一部电影吧,给我展示一下负二的平方,那将是一个挑战。

麻省理工公开课 - 电影哲学课程节选