user: Question: What is the Genre, when the Release-year of first charted record is 1968, and when the Country of origin is United States?
Columns: ['Artist', 'Country of origin', 'Period active', 'Release-year of first charted record', 'Genre', 'Claimed sales']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Metallica', 'United States', '1981–present', 1983.0, 'Heavy metal / Thrash metal', '110 million']
SQL:

assistant: SELECT "Genre" FROM "Table" WHERE "Release-year of first charted record" = 1968.0 AND "Country of origin" = 'United States';