I want to know the answer to the following question:
What milestone did Celine Dion, Mariah Carey, Phil Collins, Michael Bolton, Whitney Houston and Shania Twain share on the 1990s adult contemporary charts?
All the background I'm provided with is that "Newer female singer-songwriters such as Sarah McLachlan, Natalie Merchant, Jewel, Melissa Etheridge and Sheryl Crow also broke through on the AC chart during this time.". Is that enough to answer the question?