Lucy and Lily are twins . They are 13 years old . They look the same . But they have different hobbies . Lucy likes collecting stamps . She has many beautiful stamps . They're from different cities and countries . But Lily likes growing flowers . The flowers are all very beautiful . Lucy and Lily both like reading books . Lucy likes reading storybooks . But Lily likes reading science books . On Sunday , they usually ride bikes to the park . They can play with their friends there . Sometimes their parents go there , too .

已知引力常量G和下列各组数据，能计算出地球质量的是（   ）

以下对于某些离子的检验及结论一定正确的是(　　)