my ( $adata, $bdata );
while ( <DATA> ) {
    chomp;
    m/^A:\s*(\S)$/ and $adata = $1;
    m/^B:\s*(\S)$/ and $bdata = $1;
    m/^D:/ and do { print "A: $adata, B: $bdata\n"; last; };
}