A, B, C, according to the meaning of the question: record the positions of observed carbon particles every 30s, and then connect these positions into a broken line by straight lines in turn;

Therefore, the Brownian motion image is the position of solid particles every 30s, not the trajectory, but the connecting line of positions is recorded in turn at time intervals; So, A is wrong, B is wrong and C is wrong;

D, the chaotic motion of small solid particles is obtained from the chaotic diagram, which reflects the chaotic thermal motion of liquid molecules, so d is correct;

So choose D.