I'm not sure what you mean. The last sentence makes it clear that scientists
did in fact influence policy on nuclear testing. That part is established fact, leading the author to hypothesize that scientists could play a similar role in relation to today's challenges with geoengineering.
As for C, we're just told that a unilateral approach to geoengineering "could have detrimental consequences." There's no indication that this will involve protests.
siya1998
For question 3, option C should be correct how is the option E correct. The last paragraph says Scientists could be influential....just as .... It does a parallelization of the role that Scientists can play in creating norms for testing and deployment of geoengineering technologies.