Answer: BC and AD
Explanation: People have divided history to make it easier to study and classify a certain period of time exactly as the Bible has historically and temporally divided it, i.e. before Christ or abbreviated BC, and after Christ, AD - Anno Domini, meaning the Year of the Lord, alluding that it is about the years of our Lord Christ, means after Christ fulfilled His incarnation mission on Earth. In addition, the period before Christ, BC is also known as the before common era abbreviated BCE, and the period after Christ AD, also known as the common era, CE.