You are creating a new security policy for an application domain. You write the following lines of code. 
PolicyLevel policy = PolicyLevel.CreateAppDomainLevel（）； 
PolicyStatement noTrustStatement =   
new PolicyStatement（ 
policy.GetNamedPermissionSet（"Nothing"））；
PolicyStatement fullTrustStatement =   
new PolicyStatement（ 
policy.GetNamedPermissionSet（"FullTrust"））； 
You need to arrange code groups for the policy so that loaded assemblies default to the Nothing permission set. If the assembly originates from a trusted zone， the security policy must grant the assembly the FullTrust permission set. 
Which code segment should you use？（）