Question

Which of the following is a similarity between the verbal phrases "ir a" and "acabar de"?

Answer 1

The correct answer is A. They both follow the double verb rule even though there is a preposition in the middle, so the next verb always remains in the infinitive. 
For example: me voy a hacer eso - I am going to do that; acabo de dormir - I just stopped sleeping.
B is incorrect because they need to be conjugated, and the verb that follows does not; C is incorrect because they are normal Spanish words which would be understood anywhere where Spanish is spoken; D is incorrect because they are actually antonyms, meaning they have opposite meanings.