Researchers hypothesize that granitic soil is the ideal construction material for the desert tortoise because it is not so hard that it makes burrowing difficult or so soft that it could cause tunnels to collapse.

• Aso hard that it makes burrowing difficult or so soft that it could cause  
• Bhard enough to make burrowing difficult or soft enough as to cause  
• Cso hard as to make burrowing difficult or soft enough so it causes  
• Das hard as to make burrowing difficult or as soft as to cause  
• Etoo hard, making burrowing difficult, nor too soft, so as to cause