Among the customers from the United States, which market segment has the highest number of customers?
the highest number of customers refer to MAX(COUNT(c_custkey)); the United States is the name of the nation which refers to n_name = 'UNITED STATES'; market segment refers to c_mktsegment;
SELECT T.c_mktsegment FROM ( SELECT T1.c_mktsegment, COUNT(T1.c_custkey) AS num FROM customer AS T1 INNER JOIN nation AS T2 ON T1.c_nationkey = T2.n_nationkey WHERE T2.n_name = 'UNITED STATES' GROUP BY T1.c_mktsegment ) AS T ORDER BY T.num DESC LIMIT 1