___________ is necessary for people to develop strong bones and teeth.-考呗网

单选题___________ is necessary for people to develop strong bones and teeth.

[分析]结构识别
专有名词前一般不用冠词，calcium钙；选项C是强调句的句式，但后面需跟that，选项D是让步状语从句的一部分；而划线部分需填一个主语，因此答案为B。

1Only after food has been dried, salted or canned__________ for later consumption.

2Mrs. Lackey was awakened by the ringing of the bedside phone 12 hours after her husband's boat had been__________.

3Sales went up in the stores during December, but__________ again after Christmas.