The correct option is B To go
Option C is the correct answer as the verb ‘allowed’ needs an object to complete its meaning. The infinitive ‘to go’ is serving as an object to the verb ‘allowed.’ Also, the sentence talks about an activity supposed to happen on a certain condition. Infinitives and not gerunds are used to show suppositions. Hence, Option A cannot be used as it is a gerund. Options B and D cannot be used as they would render the sentence grammatically incorrect.