1. non-discretionary rules would make it difficult or impossible to respond to unexpected macro shocks, like changes in the velocity of money or the price of oil;

This is the correct answer, because it is part of what "activists" believe -- that discretionary policy should be used to respond to unexpected changes in macro conditions, to try and reduce the size of fluctuations.

2. it is impossible to forecast the future well enough to improve macro performance by discretionary policy;

This is a "non-activist" belief; activists believe that although forecasts can never be perfect, they can be good enough to allow discretionary policy to improve macro performance at least some of the time.

3. rules are needed to prevent manipulation of the economy for political reasons;

Again, a "non-activist" belief; "activists" tend to believe that it would be foolish to make discretionary policy (which might do much good) impossible just because it might be misused.

Again, a "non-activist" belief; "activists" tend to believe that although they do not know exactly how long time lags are, they know well enough that there will be at least some situations in which discretionary policy is more likely to improve matters than to make them worse.