Which Statement Is TRUE

Which statement is TRUE?

A) Import restrictions may be the best policy if production in certain industries generates positive spillover effects to other industries.
B) It is usually easy to identify industries that generate positive spillover effects.
C) It would be more efficient to subsidize industries that generate positive spillover effects than to implement import restrictions.
D) Spillover effects from Silicon Valley were the biggest factor leading to increases in productivity in the 1990s.