下列哪些是自然数,请把他们写在下边的横线上。0.8,223,0,0.001,400.1, 85.5, 6.768, 18
7.5-2.45+7.5+2.45(-)×21+
2.5×(1.92÷0.3-5.9) 24.5-(7.58+)
45.55-(6.82+15.55) 34.52-17.87-12.23
(×+)÷÷[(+)×]
(+)×15×11 37.5+19.5÷(2.5×4)