Reading Comprehension

I am just trying to take your views. It will be great if you can help me.

I commit nos of errors in 'according to passage' type of question in RC. I will NOT take complete passage for obvious reason but want to take a sample of the passage to share my problem:

Passage: Keyssar also scrutinizes unemployment patterns according to skill level, ethnicity, race, age, class, and gender. He finds that rates of joblessness differed primarily according to class: those in middle-class and white-collar occupations were far less likely to be unemployed. Yet the impact of unemployment on a specific class was not always the same. Even when dependent on the same trade, adjoining communities could have dramatically different unemployment rates. Keyssar uses these differential rates to help explain a phenomenon that has puzzled historians-the startlingly high rate of geographical mobility in the nineteenth-century United States. But mobility was not the dominant working-class strategy for coping with unemployment, nor was assistance from private charities or state agencies. Self-help and the help of kin got most workers through jobless spells.

According to the passage, Keyssar considers which of the following to be among the important predictors of the likelihood that a particular person would be unemployed in late nineteenth-century Massachusetts?
I. The person's class
II. Where the person lived or worked
III. The person's age
(A) I only
(B) II only
(C) I and II only
(D) I and III only
(E) I, II, and III

Answer is C but I selected D. During analysis, it became very clear that question is asking about important predictors of unemployment but while I was answering this question I somehow missed that angle completely and thought that the question is asking for factors that affected unemployment. I completely missed the angle 'scrutinizes' and 'primarily' while reading this portion of passage when I was answering the question.

My worry - how can I avoid such mistakes in future? I have just taken a note on my flash card that I need to mark each word of the two zeroed down options....but still not very sure whether this note on flash card will help. It will be great if you can give some suggestion.
Thanks
Patanjali

There is never a clear cut way of answering your question.

Practice is the only way forward. When you start your practice, underline all the important parts of the passage. That will help you go back to the important parts without having to read again.

Take down notes: One line summary of each para.

To improve your reading skills, take some editorials from the Newspaper and read on a regular basis. That will surely help you focus. You can even write down the summary of a passage after reading it.