A tow that is properly aligned to pass through a narrow opening between two bridge piers is “ （）”.

A.port and starboard strings
B.outer strings
C.drag strings
D.side strings

A.a mechanical breakdown on the tug
B.adverse tidal current conditions
C.the tug reducing its speed
D.All of the above

A.celestial meridian
B.celestial equator
C.celestial horizon
D.principal vertical circle