Explanation:

The foundation stone for the Ganga Expressway, a major greenfield infrastructure project aimed at connecting various parts of Uttar Pradesh, was laid by the Prime Minister in December 2021. Therefore, option C is correct. Options A, Unity Expressway, B, Atal Expressway, and D, Sahej Expressway, are not the names of the expressway whose foundation stone was laid in Uttar Pradesh in December 2021. These are either non-existent or refer to different projects. Thus, A, B, and D are incorrect.