Practising German grammar
Martin Durrell, Katrin Kohl and Gudrun Loftus (2011)
This grammar workbook provides a useful selection of exercises for advanced level learners who are seeking to improve the quality of their written German.
This book has been written to complement Hammer's German Grammar, but can also be used on its own.
A good source of practise for learners to work on improving the precision of their use of more complex topics such as the subjunctive.
GE GRAM 7b Open access