Which one of the following is the common element among Rajagriha, Vais

Which one of the following is the common element among Rajagriha, Vaishali and Pataliputra ?

Pali canon of the Sthaviravadins was compiled there
Ashokan Major Rock Edicts were found there
Places where Buddhist Councils were held
Places associated with the compilation of Buddhist canons of the Mahasanghikas
This question was previously asked in
UPSC NDA-1 – 2015
The correct answer is C) Places where Buddhist Councils were held. Rajagriha, Vaishali, and Pataliputra are famous in Buddhist history as the locations where the first, second, and third Buddhist Councils were held, respectively.
– The First Buddhist Council was held at Rajagriha (modern Rajgir) shortly after the Mahaparinirvana of the Buddha to preserve his teachings (Sutta Pitaka) and monastic rules (Vinaya Pitaka).
– The Second Buddhist Council was held at Vaishali about a century after the Buddha’s death to discuss controversial points of Vinaya.
– The Third Buddhist Council was held at Pataliputra (modern Patna) during the reign of Emperor Ashoka under the presidency of Moggaliputta Tissa. This council aimed to purify the Sangha and compile the Kathāvatthu (part of the Abhidhamma Pitaka).
While these cities were important centers in the Magadha empire and under Ashoka’s rule, they are most distinctly linked by having hosted these pivotal early Buddhist councils which played a crucial role in the compilation and preservation of the Buddhist canon and the early development of different Buddhist schools.