Please indicate the main function of the phrase that is in boldface in the following passage. More than one letter might be acceptable, but you must choose only one option as the best. Consider this passage from "A Piece of God's Handiwork" by Robert Redford: The BLM says its hands are tied. Why? Because these lands were set aside subject to "valid existing rights," and Conoco has a lease that gives it the right to drill. Sure Conoco has a lease--more than one, in fact--but those leases were originally issued without sufficient environmental study or public input. As a result , none of them conveyed a valid right to drill. What's more, in deciding to issue a permit to drill now, the BLM did not conduct a full analysis of the environmental impacts of drilling in these incomparable lands, but instead determined there would be no significant environmental harm on the basis of an abbreviated review that didn't even look at drilling on the other federal leases.