Question

which is a key detail that supports the main idea that there are general principles that guide sports helmet design? helmets must protect the face. helmets must not prevent seeing or hearing. scientists invent new plastics all the time. materials used for police can be used in sports.

Explanation:

The text mentions that helmets must not prevent seeing or hearing as a general principle in sports helmet design. Protecting the face is not a general principle for all sports helmets. The other two options about new plastics and police - used materials are not general design principles.

Answer:

Helmets must not prevent seeing or hearing.