I think that I have found a key of tackling assumption questions.
As per theory Assumption is an unstated evidence, and that unstated evidence is our answer. So let's put every option in the passage before conclusion and re-read the passage. If you practice the same it will take around one and half minute.
Let's see the same approach for this question.
Prephrase the passage -
65-percent response rate to ocean dumping.
On the basis of these results replace this with a word therefore, Therefore, group expects 65-70% for air pollution questionnaire.
my passage becomes -
65-percent response rate to ocean dumping. Therefore, group expects 65-70% for air pollution questionnaire.
let's put all options in the passage
A. 65-percent response rate to ocean dumping.
The group’s membership has not declined by more than 5 percent since 1987. Therefore, group expects 65-70% for air pollution questionnaire. -- Out of Scope
B. 65-percent response rate to ocean dumping.
The same number of surveys will be distributed as were distributed in 1987. Therefore, group expects 65-70% for air pollution questionnaire. -- Author is least bother about number of surveys.
C. 65-percent response rate to ocean dumping.
People who are concerned about ocean dumping are even more concerned about air pollution. Therefore, group expects 65-70% for air pollution questionnaire. - This may work hold on
D. 65-percent response rate to ocean dumping.
The response rate of one questionnaire can be predicted from that of another. Therefore, group expects 65-70% for air pollution questionnaire. - Good option Hold on
E. 65-percent response rate to ocean dumping.
The total amount of pollution today is the same as it was in 1987. Therefore, group expects 65-70% for air pollution questionnaire. -- we are least bother about this option
Now we have two options in Hand C and D. C is extreme it uses word 'more'. If you are stuck between extreme and mild option go with mild one....90% this option will be right
Therefore, IMO D