The probability of the event "4 coins, heads up, tails up" is

P=C 4 2？ ( 1 2 ) 4 = 3 8 ,

From this we can get p (ξ = 0) = c 3 0? ( 1- 3 8 ) 3 =( 5 8 ) 3 = 125 5 12 ,

P(ξ= 1)=C 3 1？ 3 8 .( 1- 3 8 ) 2 = 225 5 12 ,

p(ξ= 2)= C ^ 3 ^ 2？ ( 3 8 ) 2 .( 1- 3 8 )= 135 5 12 ,

P(ξ=3)=C 3 3？ ( 3 8 ) 3 = 27 5 12 ,

Therefore, e ξ = 0×125512+12+2×135512 = 98.

So choose B.