Misc: what is the element for the symbol Lu?

Questions

Duets - What duo had a No.1 hit with 'Too Much, Too Little, Too Late'?

Duets - Who teamed up with Celine Dion for the No.1 hit 'I'm Your Angel' in 1998?

Duets - Another real easy one! Who sang with Michael Jackson to record 'Say,Say,Say'?

Duets - Who sang a duet with Elton John that produced the hit 'Don't Let The Sun Go Down On Me' in 1991?

Duets - Dionne Warwick had a No.1 hit song, 'Then Came You,' with what artists?