Table schema:
CREATE TABLE table_name_36 (country VARCHAR, year_opened VARCHAR, span_feet VARCHAR, material VARCHAR, span_metres VARCHAR)

Question: Which country's material was concrete when the span metres were less than 270, span feet is more than 837, and the year opened was 1943?
SQL: SELECT country FROM table_name_36 WHERE material = "concrete" AND span_metres < 270 AND span_feet > 837 AND year_opened = "1943"