问题补充：
—What do you think of genetically modified food (转基因食品)?
—We all think is careless some scientists to say it is safe before doing any experiment.
A. that, for
B. it, for
C. it, of
D. that, of
答案：
A. that, for
B. it, for
C. it, of
D. that, of
解析： 考查代词与介词。句意：你认为转基因食品如何呢？我们一直认为科学家在做实验之前说这是安全的，这事是很粗心的。考查it be +adj+of sb to do，it做形式主语，真正的主语是后面的不定式，of用来表达某人品质或特性， 所以选C项。
