Enthusiasm for the use of calculators in the learning of mathematics is misplaced. Teachers rightly observe that in some cases calculators enable students to focus on general principles rather than the tedious, largely rote calculations that constitute the application of these principles. But principles are more likely to be remembered when knowledge of them is grounded in habits ingrained by painstaking applications of those principles. The very fact that calculators make calculation easier, ttherefore, makes it reasonable to restrict their use. Which one of the following, if true, most strengthens the argument? ['Some students who know how to use calculators also thoroughly understand the mathematical principles that calculators obey.', 'Slide rules, which are less technologically sophisticated analogues of calculators, were widely used in the learning of mathematics several decades ago.', 'Habits that are acquired by laborious and sometimes tedious practice are not as valuable as those that are painlessly mastered.', 'It is much more important that students retain the knowledge of general principles than that this knowledge be easily acquired.']