我又看了看m-w.com,找来他们的发音,我觉得它们读的是一样的,音标也是一样的。
http://www.merriam-webster.com/audio.php?file=class001&word=class&text=\%3Cspan%20class%3D%22unicode%22%3E%CB%88%3C%2Fspan%3Eklas\
http://www.merriam-webster.com/audio.php?file=bag00001&word=bag&text=\%3Cspan%20class%3D%22unicode%22%3E%CB%88%3C%2Fspan%3Ebag%20%3Cem%3Ealso%3C%2Fem%3E%20%3Cspan%20class%3D%22unicode%22%3E%CB%88%3C%2Fspan%3Eb%C4%81g\