Effective notes do NOT .
a. include very detailed descriptions and explanations
b. prepare you to do well on quizzes and exams
c. cover all the important points of a lecture or reading material
d. help you understand and remember concepts and facts

a. include very detailed descriptions and explanations

Explanation:

Effective notes prepared from a lecture or reading material should ideally include concise, brief, to the point explanations, laying emphasis on main headings and main concept lines.

The objective of preparing notes is to reduce massive content into small easy to recall content which can be readily referred to as per the need.

Neat, well organized, concise comprising of key words and important information would make for an effective note. Preparing lengthy notes with detailed explanations and unnecessary information would be a wasteful exercise.  

the page presents four different kinds of threats that volcanoes pose and what to do before, during, and after an eruption.