This new sports complex is _________, so people can enjoy the games whatever the season is. (A) encased (B) enclosed (C) encircled (D) enveloped
Encased would generally mean that an object or structure is fully wrapped in a solid outer layer. It also often indicates that the outer layer was created as a liquid and hardened in contact with the inner object. For example, in Empire Strikes Back, Han Solo was encased in carbonite.
Enclosed indicates that a structure or object has an outer layer that covers the entire area of the structure. It's normally only used of venues that might normally be open to the elements, such as a sports stadium. For example, technically a house with an intact roof is enclosed, but since houses normally do have intact roofs we wouldn't mention it. On the other hand, we might say that a shopping area is enclosed if what would normally be an ordinary street has a roof built over it.
Encircled commonly means that there is a distinct outer perimeter that does not come in direct contact with the structure or object. This is very commonly used in military terms, when we would say that one army encircled the other, or that a castle's keep is encircled by a curtain wall.
Enveloped has a couple of meanings. Firstly, it can indicate that something has been covered or wrapped up in something soft or flexible, such as fabric, fog, or, a bit more figuratively, a loving hug. Secondly, it can indicate the process of encircling or encasing something - as in "The Roman army enveloped the Gauls at Alesia".