Please explain

@Sidra, The author tells us that a conventional way involves tweaking one constraint while holding the rest of them constant (lines 33-39). By changing only one parameter at a time, this practice necessarily restricts the set of possible outcomes as (D) correctly points out. (A) is incorrect because it focuses on looking for a set of laws that would support life, that's relevant to the issue at hand; (B) is incorrect because it produces results; (C) is incorrect because it is false, the author acknowledges that the scientists do calculations, what-if scenarios, or computer simulations; (E) is incorrect because the author argues that this approach is too restrictive to produce a workable model. Does this help? Let me know if you have any further questions.