Other than the guadalquivir river, all other rivers in spain are not navigable because a. they cross the border into portugal b. they are not on maps of spain c. they have dangerous rapids d. they are too shallow for ships

D. they are too shallow for ships

D.they are too shallow for ships

Explanation:

The Guadalquivir river is the fifth-longest river of the Iberian peninsular and is the second-longest river in the length of Spain. Is the only great navigable river system,  has a length of 657 km and a basin size of about 56,978 km square. The primary port of this river is responsible for developing, operating and managing and marketing and the entrance of the port is protected by the locking system and protects the port from tidal influences. The port of Seville handles re than 4.9 million tones of solid bulk each day.

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Geothermic gradient is the rate of increasing temperature with respect to increasing the depth in the earths interior. away from tech tonic plates boundaries, it is about 25-40 c/km (72-87 degrees f/mi) of depth near the surface in most of the world.