单选题 Observations were made ______ the children at the beginning and at the end of preschool and first grade.
A. towards B. of C. on D. at

【正确答案】 B

【答案解析】[解析] 这里的of短语实际上应跟在observations的后面(make observations of the children)，变成被动态就成了目前这个样子，由于of的宾语太长，所以后移。