The mathematicians turned to culling periodic solutions. 数学家们转而去挑选周期解。
Culling stem cells destroys the days-old embryo harboring them, regardless of whether it was cloned or left over in a fertility clinic. 一般来讲，无论是被克隆还是被转移到其他环境中，挑选干细胞线将会自动破坏曾经养育它的胚胎。
