The best explanation of a limitation placed on the legislative branch by the Constitution is:
The legislative branch is limited by the president's ability to veto laws, though Congress can override the veto with a two-thirds vote in both chambers.
This statement accurately reflects the system of checks and balances established by the Constitution, where the executive branch has the power to veto legislation passed by Congress, while Congress has the ability to override that veto under certain conditions. The other options do not accurately represent constitutional limitations on the legislative branch.