(20 13? Mianyang Sanmao is an experimental process of screening strains that can decompose organic pollutant A efficiently from sewage treatment tanks. Based on the analysis of the following statements, A. The culture medium for separating the strains that efficiently decompose organic pollutant A is a culture medium with organic pollutant A as carbon source or nitrogen source, and the strains that cannot utilize organic pollutant A cannot grow, reproduce and form colonies due to lack of carbon source or nitrogen source; Correct.

B, the strain has strong ability to decompose organic pollutant A, and the content of organic pollutant A in the culture medium is low, so the microorganism in the culture bottle with the lowest content of substance A should be selected for further inoculation in step ③; B correct.

C, as can be seen from the title map, the purpose of inoculation process ④ is to separate and purify strains that can decompose organic matter A; C is correct.

D. The purpose of repeating the process ⑤ for many times is to expand the culture and obtain more target bacteria, instead of improving the ability of bacteria to decompose organic matter A; D error.

Therefore, choose: d.