99色精品-9色在线-99色在线-99色视频 国产欧美日产一区二区三区_亚洲精品亚洲人成在线观看_四虎在线精品永久观看_免费一级a一片久久精

單項選擇題

The nominal range of a light may be accurately defined as the maximum distance at which a light may be seen().

A.under existing visibility conditions
B.under perfect visibility
C.with ten miles visibility
D.with fifteen miles visibility

微信掃碼免費搜題