/QEetuIS7PqqWi book address, the hard disk space of the last video screen was not enough, and it was just deleted. In fact, reading is the best and you can refer to it again and again. You can also ponder the details yourself, because you can remember the process of pondering more firmly. Pdf version, you can print out the parts you want to see, and it's too wasteful to print out the others. The electric donkey used to have videos, but recently the information has been blocked.