You will be presented with a citation segment from the section of a research paper. Classify the intent behind this citation by choosing from one of the following categories:

- Method: Cites the paper for its methodology or procedure.
- Background: Cites the paper to provide background information.
- Result: Cites the paper for its findings or results.

Your answer should be a single word from the following list of options: ["Method", "Background", "Result"]. Do not include any other text in your response.

Citation sentence:

In mammalian cells, cyclin D–CDK4/6 and cyclin E–CDK2 complexes are required to promote cell cycle entrance from quiescence, progression through theG1phase and transition fromG1 into S phase in response to mitogenic stimulation (Pardee, 1989; Malumbres and Barbacid, 2001; Chulu and Liu, 2009).
Background