You are entering port and have been instructed to anchor，as your berth is not yet available．You are on a SW'ly heading，preparing to drop anchor，when you observe the range lights as shown on your starboard beam．You should ______．

A、not drop the anchor until the lights are in line
B、ensure your ship will NOT block the channel or obstruct the range while at anchor
C、drop the anchor immediately as the range lights mark an area free of obstructions
D、drop the anchor immediately as a change in the position of the range lights will be an indication of dragging anchor