When using science to investigate physical phenomena, which characteristic of the event must exist

I think you forgot to give the options along with the question. I am answering the question based on my research and knowledge. "Observable" is the one characteristic of event that must exist when using science to investigate physical phenomena. I hope that this is the answer that has come to your help.

Where's the pictures ?

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.