Would it be alright if you pasted the story? Thanks ^_^
In this excerpt the narrator is complaining about the way achievement test are and how up to that they measure someone’s knowledge. He uses the word bland to describe the right answer of this kind of tests which it means „lacking a strong or particular flavor; not interesting”, in this context can be used describing it as non-sense or not obvious answers. He also complains about how bad he is in this because he cannot find the logic in the answers. With this explained, we can infer that the right answer is D Tan believes that achievement tests give inflated measurements of language ability, because he kind of argues that the answers are not "valid" to measure it.
Suppose
Here's a link to help you further
http://writingexplained.org/suppose-vs-supposed-difference
