单选题 In order to stay warm during an extended period of time exposed to frigid weather a big heavy coat worn over normal clothing is not always the best method. If you are going to be spending a ______ period in the cold it is much better to dress in several lighter layers rather than in one heavy layer. By wearing layers the clothing acts ______ containment system for warmth. It takes body heat longer to escape layers than it does to escape one heavy layer. In addition, wearing a hat is recommended because most body heat is lost through the head and mittens are ______ to gloves.