Taichi, an electric car brand, is known for its excellent autonomous driving capabilities and reduced emissions. However, most of its users complain of certain technical issues after a period of one year. The company is well aware of these issues because it has deliberately designed these products to fail after a certain period$-$a strategy to generate revenue through service charges. In the context of business behavior, Taichi's business conduct is

legal but unethical

illegal but ethical

illegal but unethical

legal but ethical