Large areas of grazing land were turned into game reserves
- This statement is true. In the early 20th century, large areas of grazing land in Tanzania were converted into game reserves to protect wildlife populations and promote conservation efforts. This was a result of the colonial policies implemented by the British government in East Africa.

Pastoralists were not allowed to enter these reserves
- This statement is true. As game reserves were established, pastoralists, such as the Maasai people who traditionally relied on these lands for grazing their livestock, were prohibited from entering these areas. This restriction was enforced to prioritize wildlife conservation and prevent potential conflicts between wildlife and livestock.

Serengeti National Park was created over 14,760 km of Maasai grazing land
- This statement is true. Serengeti National Park, one of the most famous wildlife reserves in Africa, was established in 1951. It covers an area of approximately 14,760 square kilometers and spans across Tanzania and Kenya. Prior to its establishment, this land was traditionally used by the Maasai for grazing their livestock.

Explanation:
During the colonial period, the British government implemented policies that aimed to protect wildlife and establish game reserves in East Africa. This led to the conversion of large areas of grazing land into these reserves, which restricted the access of pastoralist communities, such as the Maasai, to their traditional lands.

The creation of Serengeti National Park in 1951 further restricted the Maasai's access to their grazing lands. The park was established over a vast expanse of Maasai grazing land, spanning across Tanzania and Kenya. This had a significant impact on the traditional way of life for the Maasai people, as they were no longer able to freely graze their livestock in these areas.

Overall, the statements a), b), and c) are all true. The conversion of grazing land into game reserves, the prohibition of pastoralists from entering these reserves, and the creation of Serengeti National Park over Maasai grazing land were all part of the conservation efforts and policies implemented in Tanzania.