A simple rule for picking committee chairs in effect until the 1970s. The member who had served on the committee the longest and whose party controlled Congress became the chair, regardless of party loyalty, mental state, or competence.

Seniority system.

Explanation:

Seniority System was the term used to define the rule of the special perks or benefits credited to the members of the Senators and the House of the Lords.

According to this rule, members of the Congress, who have served the longest in the government were benefited with special perks such as they get to choose for themselves their offices and committee assignments.

In this rule, committee assignments were the most important perk that the members get as many legislative works of importance are held in these assignments only.

So, the correct answer is the seniority system.

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