Step 1 : Introduction to the question "3. '... in the Sky with Diamonds' was sung by the Beatles. Who is the lady in hiding here?"
...1. Lucy 2. Sandy 3. Mary 4. Connie 'Lucy in the Sky with Diamonds' was written primarily by John Lennon and credited to Lennon/McCartney. It was included in The Beatles' 1967 album 'Sgt. Pepper's Lonely Hearts Club Band'. I found an interesting article on Wikipedia that I would like to share with you: "A 3.2 million year-old, 40% complete fossil skeleton of an Australopithecus afarensis specimen discovered in 1974 was named 'Lucy' because The Beatles' song was being played loudly and repeatedly on a tape recorder in the camp. The phrase 'Lucy in the skies' became 'Lucy in disguise' to the anthropologists, because they initially did not understand the impact of their discovery."
Step 2 : Answer to the question "3. '... in the Sky with Diamonds' was sung by the Beatles. Who is the lady in hiding here?"
Please let us know as comment, if the answer is not correct!