The first is risky, the second is unstable, and the third is not as simple as you think. Blackening optical technology needs resources and capabilities. There is also that everyone has different ideas and is unwilling to do it. Besides, let's talk about cracer here. He is a big fool. I spent more than 10 thousand yuan learning from him before, so I didn't study at home for several months. Xiao Di's video is deeper than Crather's!