Which one of the following types of roofing can be used to make closed valleys?

Closed valleys are a roofing technique where the roofing materials meet at a valley without the use of a separate metal flashing. Asphalt shingles are particularly suited for this application due to their flexibility and the way they can be installed in overlapping layers. When installed properly, asphalt shingles can create a watertight seal in the valley, effectively directing water off the roof without the risk of leaks that might come from using other materials.

In contrast, clay tiles, wood shakes, and wood shingles do not lend themselves easily to closed valleys. Clay tiles often require a metal flashing to prevent water infiltration due to their rigid structure and installation method. Wood shakes and shingles may also necessitate a different installation technique to ensure proper water runoff, typically utilizing flashing to protect vulnerable areas from moisture. Thus, asphalt shingles are the most compatible choice for creating closed valleys in roofing applications.