1. Kev tiv thaiv overload 2. Kev tiv thaiv luv luv 3. Tswj 4. Siv nyob rau hauv lub tsev nyob, lub tsev tsis nyob, lub zog ntawm kev lag luam thiab infrastructure. 5. Raws li hom instantaneous tso tawm raws li nram no: hom B(3-5)ln, hom C(5-10)ln, hom D(10-20)ln