Those who fear the influence of television deliberately _____ its persuasive power, hoping that they might keep knowledge of its potential to effect social change from being widely disseminated.

The above highlighted are the clue to solve the above question.

So in simple terms, Those people who fear the influence of TV deliberately __ its persuasive power (This part indicates that these people are doing something not very favorable) hoping, to keep knowledge.. from being widely disseminated.

I can use a words like hinder or understate or spread a negative word about it. On to the options:

promote- Opposite- OUT
underplay- Hold matches the above prediction
excuse- Not relevant- OUT
laud- Not relevant- OUT
suspect- Not relevant- OUT


IMO B

Hope this helps!