If Congress questions how the Department of Energy is enforcing the policy on disposal of nuclear waste, Congress can use to call a hearing to question Department of Energy officials on the results of a congressional investigation.

Its oversight function

Explanation:

 According to the given question, the congress can using its oversight function for monitoring supervising and also reviewing all its activities, policies implementation process and functions.

 The main purpose of  department of energy is that it helps in advancing the economical and the national securities by implementing various types of policies.

According to the given question, the oversight function plays an important role for developing various types of legislative proposal in the department of energy. Therefore, Its oversight function is the correct answer.  

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