What was the U.S birthstone in the 15th-20th century when in 2013 it was amethyst?
CREATE TABLE table_name_34 (us__2013_ VARCHAR)
SELECT 15 AS th__20th_century FROM table_name_34 WHERE us__2013_ = "amethyst"
<s>[INST] Write mssql query to answer the following question given the database schema. Schema: CREATE TABLE table_name_34 (us__2013_ VARCHAR) Question: What was the U.S birthstone in the 15th-20th century when in 2013 it was amethyst? [/INST] SELECT 15 AS th__20th_century FROM table_name_34 WHERE us__2013_ = "amethyst" </s>