A:arrived at
B:topped at
C:reached to
D:came to
一个古生物学家研究岩石层中的化石层,鉴定出一个物种。他认为这个物种在一个较长的历史年代中没有发生什么变化。他做出这个判断的依据是()
May we leave the classroom now? No, you _____. You_____ to leave until the bell rings.