Well, Snappy, option (b) is a true statement. If you'll allow an appearance as a back-up singer to count. Cissy Houston, indeed, sang back-up on daughter Whitney's 1987 #1 "I Wanna Dance With Somebody". She also sang back-up on Presley's 1969 "Suspicious Minds" which went very close to the top. Well, #2, which is as close as you can go.
And I'm very damn sure there was a mother-son combo in the 1970s. I'm just having a very hard time nailing it down. Ten years is a dang lot of #1s!
So, if we're counting back-up singers, all four statements are true! Which is of academic interest only, because, obviously, back-up singers weren't included when the question was framed
And I'm very damn sure there was a mother-son combo in the 1970s. I'm just having a very hard time nailing it down. Ten years is a dang lot of #1s!

So, if we're counting back-up singers, all four statements are true! Which is of academic interest only, because, obviously, back-up singers weren't included when the question was framed
Comment