In the experiment of measuring the acceleration of gravity with a simple pendulum: (1) This experiment is based on the formula g=4π2lT2g=4π2lT2(2).

(1) From the periodic formula of a simple pendulum: T=2πlg,

Gravity acceleration: g=4π2lT2,

(2) The time for a simple pendulum to complete n times of total vibration is t, so t = TN. According to T=2πlg, g = 4π 2LT2 = 4π 2N2LT2.

(3) Solution: A. From the period T=2πlg of the simple pendulum, we can get that the acceleration of gravity is g=4π2lT2, which shows that the acceleration of gravity has nothing to do with the mass of the pendulum ball, so A is wrong.

B, when calculating the pendulum length, take the catenary length as the pendulum length, and the pendulum length should be the catenary length plus the radius of the ball, from which a small L can be obtained. From the gravitational acceleration of g=4π2lT2, it can be seen that the gravitational acceleration is small, so B is wrong.

C, the total vibration of n times is mistakenly recorded as (n+ 1), and the actual period should be: T=tn, which leads to the period being smaller than the actual period. It can be seen from the gravitational acceleration of g=4π2lT2 that the gravitational acceleration is too large, so C is correct.

D, according to the expression of gravity acceleration, has nothing to do with the swing angle, so D is wrong.

So choose: C.

Therefore, the answer to this question is: 4π2lT2, 4π2n2lt2, C.