试题题干
WORD FORMATION
Complete the following sentence with the proper form of the word in the bracket.
(sure) The clients must 
that accurate records of consumption are kept for at least one month.
参考答案
试题解析
此处缺少动词。
must是情态动词，情态动词后用动词原形，所以填sure的动词形式ensure。
句意：客户必须确保准确的消费记录保存至少一个月。