human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Call sign, Frequency MHz, City of license, ERP W, Class, FCC info
###Question: Class of d, and a Frequency MHz smaller than 107.7, and a ERP W smaller than 232 has what call sign?
gpt
SELECT Call sign FROM table WHERE Class = d AND Frequency MHz < 107.7 AND ERP W < 232