Why do streams flow almost in one direction in a parallel pattern?

Correct answer: Due to steep and uniform slope

The direct answer is A: streams flow nearly in one direction in a parallel pattern because the land has a steep and fairly uniform slope. A drainage pattern is controlled by the shape and structure of the surface. On a strong, similar gradient, streams tend to follow the same downhill direction, producing roughly parallel channels and tributaries. Option A is correct because it identifies slope as the controlling factor. Option B is wrong because low rainfall and a closed basin may affect the amount of water or the drainage arrangement, but they do not define a parallel pattern. Option C is wrong because right-angled fractures commonly produce a rectangular drainage pattern, not a parallel one. Option D is wrong because heavy delta deposition concerns the river mouth and does not explain parallel streams across a sloping surface. The pattern may not be perfectly straight, but the common direction is the important clue. Memory cue: parallel lines on a map usually point to a common slope.