①Garbage should be collected in categories. Domestic garbage that causes "white pollution" should be placed in garbage cans with a ______ (fill in the letter) mark. ②Industrial wastewater

(1) "White pollution" domestic waste is recyclable waste,

So choose: a;

(2) Cadmium removal by polyaluminum chloride The principle is that the aluminum salt is hydrolyzed to form aluminum hydroxide colloid to absorb cadmium ions, which is a new and efficient coagulant and water purifier.

So the answer is: b;