A.a△b means that the operation is a-(a+1)+(a+2)-(a+3)+(a+4)-... with B * * participating in the operation;

So 1 10 △ 3 is10-1+12 =11,

②x△7 is x+3=2003,

So x=2000.

B. first a≠0, then a+b=0, so b

/a

=- 1, b= 1, a=- 1, so a+3b = 2. So the answer is: 2.

C.

A can't be 0, so D can't be 0, so A and D can be 1, 2, 3, 4, 5, 6, 7, 8, 9 and * *, and B and C can be 0, 1, 2, 3, 4, 5, 6, 7.

So the four-digit symmetry number * * * has 9× 10=90 (pieces).

It's really abnormal. . .