Is often the target of criticism in invasion literature.
a. education spending
b. economic policy
c. the election process
d. military strength

D). Military strength.

Explanation:

Invasion literature was highly popular during the late 19th century and early 20th century(during world war I). Such literature offered the perturbation led by the speculative invasions of foreign powers. The writings of this literature were inclined towards criticizing 'military' strength through the creation of war imageries. This type of literature investigates the nation's potential to counter the pounce/attack which was greatly influenced by the German attack/invasion of England. Thus, option D is the correct answer.

it is an infinitive phrase with a subject.

hm, switch the relative; nominative and indefinite; objective ? not too bright in the knowledge of the english.