List the full name of all the senior senators in year 2013.
full name refers to official_full_name; senior refers to state_rank = 'senior'; senators refers to type = 'sen'; 2013 refers to start LIKE '2013%'
SELECT T2.official_full_name FROM `current-terms` AS T1 INNER JOIN current AS T2 ON T2.bioguide_id = T1.bioguide WHERE T1.state_rank = 'senior' AND T1.type = 'sen' AND T1.start LIKE '2013%'