The function of making laws is not a responsibility of the executive branch; this duty lies with the legislative branch. The executive branch, however, does have responsibilities in the implementation and enforcement of laws.
The main answer to your question is 'b. making laws'. The legislative branch, which comprises the U.S. Congress in the American Constitution, has the inherent responsibility of making laws; it's not a responsibility of the executive branch. However, the executive branch, led by the President, does play a critical role in the law-making progress by proposing bills, suggesting budgets, and having the power to approve or veto legislation passed by the legislature.
The executive branch is indeed responsible for implementing and enforcing laws, which are choices 'c' and 'd' respectively, as part of its duties. It ensures that the laws are properly carried out on a daily basis. For instance, if we look at the example of laws relating to gun control given in the reference, the President can create a commission to review the problem and make recommendations, including implementation through executive orders if necessary.
In conclusion, whereas the executive branch has the capacity to influence and execute laws, the clear-cut responsibility of actually making laws falls under the ambits of the legislature (i.e. 'making laws' is not a function of the executive branch).
Learn more about Executive Branch Responsibilities