补全短文
At least one out of every five elementary school students in the US has trouble learning to read, even when the students are good at other subjects. ________.
A、Many adults are interested in matching sounds with letters.
B、The students also practiced reading aloud and spelling.
C、In lower level readers, this structure remains inactive.
D、The biggest challenge for many of these kids, scientists say, is matching sounds with letters.
【正确答案】 D
【答案解析】 第一个句子说的是：在美国五个小学生中至少有一个在学习阅读方面有困难，虽然这些学生其他科目都不错。这是一个总的说明，接着的句子应该具体化了。D就是进一步的说明：科学家说，这些孩子中的许多人的最大困难是如何使得读音和字母对应起来。