Which type of river is more useful for navigation?

Correct answer: A deep and slow flowing river

The direct answer is A, a deep and slow-flowing river. Navigation means travelling by boats or ships on water. A navigable river needs enough depth for the boat to float without touching the bed, and a comparatively gentle current makes steering and movement safer. A broad, fairly clear channel and fewer rocks or sudden drops also help, although the question asks for the best general type. Option A is correct because depth provides water space for boats and slow flow makes travel easier to control. Option B, a very shallow and rocky river, can damage boats and make movement difficult or impossible. Option C, a completely dry river, has no water in which a boat can travel. Option D, an underground river, is generally inaccessible and unsuitable for ordinary surface navigation. The reasoning is: navigation needs continuous water, sufficient depth and manageable speed; only option A gives the essential conditions. A slow river is not necessarily always navigable, but among these choices it is clearly the most useful. Exam cue: for river transport, remember ‘deep water and gentle current’.