Another technical challenge in environmental protection is how to shorten the aeration time in the biochemical reaction tank during the sewage treatment process to improve the sewage treatment speed. One of the solutions is to find more suitable microorganisms in the activated sludge; the other method is An enzyme is added to the sludge to speed up the reaction speed. The enzyme acts as a catalyst in the biochemical reaction and will not reduce itself. However, recovering the enzyme from biological products and sludge is a difficult problem. Magnetic separation technology can also come in handy here: using the magnetic susceptibility difference of enzymes and sludge, they can be separated by a high gradient separator. At the same time, a certain intensity magnetic field can promote the growth and reproduction of some microorganisms, thereby making the sewage The microorganisms in the mud increase the reaction speed and speed up the sewage treatment. Which of the following shows that one of the real functions of magnetic separation technology in wastewater treatment is? ['Shorten the residence aeration time in the biochemical reaction tank during the sewage treatment process to improve the sewage treatment speed.', 'Promote the growth and reproduction of microorganisms in sludge, increase the reaction speed of microorganisms, and speed up the treatment of sewage.', 'Use a high gradient magnetic separator to separate the enzymes with different susceptibility from the sludge, thereby recovering the enzymes in the sludge.', 'Find more suitable microorganisms in the activated sludge or add an enzyme to the sludge to speed up the reaction speed of the sewage.']