A. Christa chose to write a literary critique of the novel <em>Oliver Twist</em>.
An infinitive phrase will include the word “to” in addition to a verb. For instance, “to run,” “to sleep,” and “to laugh” are all infinitives. If the word “to” is followed by a noun, “to” would be a preposition. And, an object is the recipient of the action/verb. With that in mind, in Option A we can see that “to write” is receiving the action “chose,” which makes “to write” a direct object.
The only sentence here with an infinitive phrase is the first one, and the infinitive phrase there is 'to write'. You ask the question - What did Christa choose? in order to find the object of that sentence, and the answer is 'to write'.
