B for me.
The question is trying to say "usually the private residences of the head of the states are not that accessible"."but white house is accessible"
A seems to indicate white house was not accessible before but now it is more accessible. it does not compare it with other private residences.
C and D are obviously incorrect. "than has" is awkward and "than one" seems to indicate a person.
E. seems wordy...the "it" here refers to the white house which is present in the sentence. so unnecessary
this time, we play for keeps