A(n) was a military fort that protected the missions,
a infantry
b. valero
c. encroachment
d. presidio

A. Presidio

Explanation: a presidio is the military near missions to protect it. God bless you.

the three answers (for plato at least) are:

b-condemned sola fida 

d-set rules for establishing seminaries and for educating clerics in the seminaries 

f-recommended moderation in the sale of indulgences and banned the sale of false indulgences 

the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.