Dear friends, I teach adult students levels from A1 to B2, I would like you to give me some advice about what books you consider essential material  to have in the department to teach them,  related to skills and grammar. For example I find very useful books such as:
 
 Grammar: Dereck Grammar World. Black cat
Listening: extra listening . C.U.P
Writing: Sucessful Writing. Express Publishing
 
Thanks in advance