12.地球的表面积约为511000000km2,511000000用科学记数法表示正确的是( )
0 283015 283023 283029 283033 283039 283041 283045 283051 283053 283059 283065 283069 283071 283075 283081 283083 283089 283093 283095 283099 283101 283105 283107 283109 283110 283111 283113 283114 283115 283117 283119 283123 283125 283129 283131 283135 283141 283143 283149 283153 283155 283159 283165 283171 283173 283179 283183 283185 283191 283195 283201 283209 366461
| A. | 0.511×109 | B. | 5.11×108 | C. | 51.1×107 | D. | 511×106 |