First, each square consists of four small squares, each square has four directions (some of which are the same), which correspond to four complementary sets (that is, if it is put down, it will just become flat). Each square is searched and filled first, and if it fails, it will be leveled to the lowest value;

Second, you can't, because Tetris has five modes. If all the combinations appear, you will have five right-handed modes after playing for 72 hours and 26 minutes. Second, you can't erase them

Third, no, the answer is as above.

Fourth, think through enumeration and combination.

Ps: It took me three hours. Give me extra points!