GMAT Sentence Correction (SC) | Re: The Queensway Tunnel was built in the 1930s

Hi,
According to Manhattan Sc, all 'it, its' refer to the same singular antecedent in a sentence and all 'they, them, their' refer to the same plural antecedent in a sentence. We clearly know from the non-underlined portion of the sentence that 'it' refers to 'tunnels'. Thus. all 'it or its' in the sentence must refer to 'tunnel'. I have not seen a single question defying this rule.
Though I agree option (d) says that 'tunnel was carrying', but apparently, this is the best option at hand.
Also,