Ifyourpenbrokeatschooltoday,whatwouldyoudo?Youwouldgoto...
问题详情：Ifyourpenbrokeatschooltoday,whatwouldyoudo?Youwouldgotoashopandbuyanewone.Whatifyoucouldsimplyprintoutareal,workingpenwithyour3-Dprinterwithoutleavingyourroom? Tenyearsagopeoplecouldonlys...