The correct option is D 7
The common difference of the arithmetic progression 12,19,26,33,... is 7. When 6 is subtracted from each of its term, the common difference of the resulting A.P. is the same. This can also be seen from the resulting A.P. The new A.P. is 6,13,20,27,... Thus the common difference of the new A.P. is also 7. Therefore, the correct answer is 'd'.