what's party with district being pennsylvania 21
CREATE TABLE table_18253 (
    "District" text,
    "Incumbent" text,
    "Party" text,
    "First elected" real,
    "Result" text,
    "Candidates" text
)
SELECT "Party" FROM table_18253 WHERE "District" = 'Pennsylvania 21'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: what's party with district being pennsylvania 21 ### Input: CREATE TABLE table_18253 (
    "District" text,
    "Incumbent" text,
    "Party" text,
    "First elected" real,
    "Result" text,
    "Candidates" text
) ### Response: SELECT "Party" FROM table_18253 WHERE "District" = 'Pennsylvania 21'