Final answer:
The first missionary center established by Guru Nanak Dev Ji was at Kartarpur, which became the central hub for spreading the teachings of Sikhism.
Step-by-step explanation:
The first missionary center (Manji) established by Guru Nanak Dev Ji was at Kartarpur. Guru Nanak Dev Ji was the founder of Sikhism and the first of the eleven Sikh Gurus. Kartarpur became a central religious hub where Sikhism's foundational teachings were spread. It was here that Guru Nanak settled after his missionary travels and started a community with a new way of life based on the principles he taught. The first missionary center (Manji) established by Guru Nanak Dev Ji was in A) Kartarpur. This center served as a place where Sikhs could come together to practice their faith and associate with each other.