Correct Answer: E
Explanation:
There are two main issues being tested in this problem.
(1) The subject (executive managers, which is plural) must be referred to with a plural pronoun (them not it)
(2) The Board of Directors planned to do two things: to fire the current executive managers and [to] replace them. These two plans must be parallel.
The resulting sentence is: the Board of Directors planned to fire the current executive managers...and [to] replace where the [to] is understood since replace is in the infinitive form.
A. the phrase the Board of Directors planned to fire...and in replacing is not parallel
B. the singular pronoun it cannot refer to a plural subject (i.e., the current executive managers); the phrase to be replacing is not concise and should be replaced by to replace
C. the singular pronoun it cannot refer to a plural subject the current executive managers
D. the phrase the Board of Directors planned to fire...to replace lacks the word and, which is needed to clearly delineate between the two actions or plans that the Board announced
E. the phrase the Board of Directors planned to fire...and replace is parallel; the plural pronoun them correctly references a plural noun (i.e., current executive managers)