Answer : 4. "10!/2"
Explanation :

Answer: D) 10!/2 Explanation: As A1 speaks always after A2, they can speak only in  1st  to 9th places and    A2 can speak in 2nd to 10 the places only when A1 speaks in 1st place    A2 can speak in 9 places the remaining     A3, A4, A5,...A10  has no restriction. So, they can speak in 9.8! ways. i.e   when A2 speaks in the first place, the number of ways they can speak is 9.8!.   When A2 speaks in second place, the number of ways they can speak is  8.8!.   When A2 speaks in third place, the number of ways they can speak is  7.8!. When A2 speaks in the ninth place, the number of ways they can speak is 1.8!       Therefore,Total Number of ways they can  speak = (9+8+7+6+5+4+3+2+1) 8! = 92(9+1)8! = 10!/2