题目

Last year I ruined my summer vacation by bringing along a modern convenience that was too convenient for my own good: the iPad. Instead of looking at nature, I checked my email. Instead of paddling a small boat, I followed my Twitter feed (推特简讯). Instead of reading great novels, I stuck to reading four newspapers each morning. I was behaving as if I were still in the office. My body was on vacation but my head wasn’t. So this year I made up my mind to try something different: withdrawal (退出) from the Internet. I knew it wouldn’t be easy, since I’m bad at self-control.（4分）钙是人体必须的常量元素，每日必须摄入足够量的钙．目前市场上的补钙药剂很多，下图是某种品牌的补钙药品的部分说明书．请回答下列问题：（1）CaCO3中各元素的质量比； （2）CaCO3中钙元素的质量分数； （3）若每片钙片的质量为0.5g，则钙片中钙元素的质量分数；（4）如果按用量服用，每天摄入钙元素的质量。