Anticipated Objections and Rebuttals
When writing an argument, writers must anticipate any objections their audience might use to challenge that argument. In other words, they have to make sure, to the best of their ability, that they don't leave room for their audience to pull a card out of one of the levels of their "house of cards" (thereby causing the whole structure of the argument to tumble down). In this argument, the writer has addressed two possible oppositional arguments, one having to do with availability of information on alternative grasses, and one having to do with the cost of switching to alternative landscaping.