Cov Tswv Cuab Lub Qhov Rooj Part 2

Rau qhov rooj sab hauv uas muaj cov khoom nyab xeeb hluav taws xob, tab sis tsis yog hluav taws kub, xav txog cov khoom khov kho sab hauv qhov rooj. Cov pob tub ntxhais tsis muaj cov ntoo, tab sis lawv muaj cov hluav taws xob ntxhiv lossis cov khoom ua suab nrov zoo nkauj thiab muaj zog dua li lawv cov khoom siv hollow. Txij li muaj ntau ntxiv rau lub qhov rooj kom hlawv los ntawm ntau lub hollow core me core qhov rooj, lawv muaj kev tiv thaiv hluav taws me me ntxiv.