Plant growth regulators are a class of substances that have inhibitory or promoting effects on the growth and development of plants, including artificially synthesized compounds and natural plant hormones extracted from organisms. They are currently widely used in agricultural production worldwide. In case of doubt, industry insiders pointed out that according to the results of batch testing, the presence of plant growth regulators could not be seen. Therefore, the safety of plant growth regulators can be considered to be more reliable. Which of the following is true is most likely to question the views of those in the industry:. ['After spraying the plant growth regulator, it will exist in the soil for a long time and it is not easy to decompose.', 'Some developed countries have strict regulations on the use of plant growth regulators.', 'From past experience, even widely used products may not be safe.', 'Some plant growth regulators may cause disease even if the content is not detected.']