三角形内角之和等于180°,这是古希腊数学家欧几里得提出的定理。在此之后的两千多年里,人们一直把它当作任何条件下都适用的真理。但是,19世纪初,俄国数学家罗巴切夫斯基提出:在凹曲面上,三角形内角之和小于180°。随后,德国数学家黎曼提出:在球形凸面上,三角形内角之和大于180°。这说明真理是( )①因人而异的 ②具体的 ③有条件的 ④客观的
I know you don’t like __________ music very much. But what do you think of __________ music in the film we saw yesterday?
Everywhere man has cut down __________ forests in order to grow crops, or to use __________ wood as fuel or as building material.
For him __________ stage is just __________ means of making a living.
Of all __________ reasons for my decision to become a university professor, my father’s advice was __________ most important one.
In __________ review off 44 studies, American researchers found that men and women who ate six key foods daily cut the risk of __________ heart disease by 76%.