[概括大意]It is not difficult to think of other messages we receive through the mass media. Every day we get hundreds of them. Think about advertisements， for example. We see and hear these messages almost everywhere we go. Advertisements are important messages， even though they are sometimes annoying. They help us compare and evaluate products.
The main idea of this paragraph is__________.
A、Importance of the Mass Media
B、Media — Means to Communicate Messages
C、Advertisements as Important Messages from the Mass Media
D、Various Messages One May Receive Each Day
答案解析：选项借用了段中的词 Advertisements、important messages。本段主要介绍了广告是大众媒体的重要媒介。
[填句补文]He has also included symbols to show which ions are nutrients， and which are common in soil or water. ________.
A、There have been many attempts to redesign the periodic table since Dmitri Mendeleev drew it up in 1871.
B、And the size of element‘s symbol reflects how much of it is found in the Earth’s crust.
C、Railsback has still ordered the elements according to the number of protons they have.
D、Raisback has listed some elements more than once.