Before the primary school can open to the public in time for the fall semester

Before the primary school can open to the public in time for the fall semester, the crew in charge of the project must finish construction, cleaning, and safety-proofing it’s interior.

1. must finish construction, cleaning, and safety-proofing it’s interior
2. must finish construction of, cleaning, and safety-proof its interior
3. must finish constructing, cleaning and safety-proofing it’s interior
4. must finish constructing, cleaning, and safety-proofing its interior
5. must finish construction, cleaning and safety-proofing the interior

Answer

Two problems exist in this sentence. 

1. The use of it’s (the contraction of it is) instead of the possessive form its. Eliminate Choices A and C.

2. Check parallel structure in the underlined list. All projects must share the same grammatical form. Choices B and E improperly mix the noun construction with the gerund forms of cleaning and safety-proofing, and Choice E improperly defines construction as cleaning and safety-proofing the interior.

The correct option is D.