Simple Maths

9.Which of the following is incollect ?
A. Starting from the second term of a sequence , if the different obtained by subtracting the previous term from each term is fixed then the sequenceis an arithmetic sequence .
B. Starting from the second term of a sequence , if each term is greater than the previous term , then the sequence is a geometric sequence .
C. 1 is a triangular number .
D . 1 is a square number.