The correct answer is option 'C' - Cabinet.

Explanation:
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The substance and timing of a bill are determined by the Cabinet. The Cabinet is a group of high-ranking government officials, usually appointed by the President or Prime Minister, who are responsible for making important policy decisions and advising the head of government.

1. Role of the Cabinet:
The Cabinet plays a crucial role in the legislative process by formulating and proposing bills to be presented to the legislative body for consideration. They are responsible for the drafting and development of bills, including the determination of the content, scope, and objectives of the proposed legislation.

2. Substance of the Bill:
The Cabinet members, who are experts in their respective fields, analyze the issues and needs of society and then propose bills that address these concerns. They discuss and debate the various aspects of the bill, ensuring that it aligns with the government's policy objectives and priorities. The Cabinet's collective expertise and knowledge help shape the substance of the bill, ensuring that it is comprehensive, effective, and reflects the government's agenda.

3. Timing of the Bill:
The Cabinet also determines the timing of when a bill should be introduced to the legislative body. They consider various factors such as the urgency of the issue, political climate, public opinion, and the government's agenda. The timing of the bill is crucial as it can affect its chances of success in the legislative process. The Cabinet's decision on the timing ensures that the bill is introduced at an opportune moment to maximize its chances of receiving support and passing into law.

4. Consultation and Approval:
Before finalizing the substance and timing of a bill, the Cabinet engages in extensive consultations with relevant stakeholders, including experts, interest groups, and other government departments. This allows them to gather diverse perspectives and consider the potential impact and implications of the proposed legislation. Once the bill is finalized, it is presented to the legislative body for approval and further debate.

In conclusion, the Cabinet, comprising high-ranking government officials, holds the authority to decide the substance and timing of a bill. They utilize their expertise, consult relevant stakeholders, and consider various factors to ensure that the proposed legislation aligns with the government's policy objectives and is introduced at an opportune moment.