Normal refraction causes waves to:

Normal refraction describes the phenomenon where waves change direction as they travel through different mediums, but the term 'normal' also implies that these waves typically move straight when entering a homogenous medium. This principle is based on the way light behaves when passing through materials of differing density, and similar concepts apply to water waves. When a wave crosses into a region where its speed changes (for example, due to variations in water depth), refraction can cause bending, but in its most straightforward sense, when discussing normal refraction, the primary movement is indeed straight.

In navigational terms, this understanding is crucial for predicting how waves will behave in different environments, especially when approaching shorelines, obstacles, or varying water depths. The other choices highlight different behaviors of waves under certain conditions or forces, but they do not encapsulate the primary characteristic of normal refraction, which is maintaining a straight line under constant conditions.