The best answer is mattress. The relationship between the first pair of words, BARN and FARM, is that of part to whole—one word is a part or piece of the other. Therefore, the second pair of words must also have a part-to-whole relationship. A mattress is part of a bed.
Warning: include(Mobile_Detect.php): failed to open stream: No such file or directory in /site/html/template/www.infoplease.com/trailer.php on line 412
Warning: include(): Failed opening 'Mobile_Detect.php' for inclusion (include_path='/site/lib/vendor/pear-pear.php.net/Mail:/site/lib/vendor/pear-pear.php.net/Net_Socket:/site/lib/vendor/pear-pear.php.net/Net_SMTP:.:/site/lib:/site/vendor:/usr/share/pear:/usr/share/php:/site/html') in /site/html/template/www.infoplease.com/trailer.php on line 412