IGNORE THIS:
"Install Step :
1.Download the English Grammar in Use v1.11.40 MOD APK File.
2. Extract & Move ZIP File (com.xxx folder) to Android/OBB folder in your device.
3. Install MOD APK.
4. Enjoy."
SIMPLY DO THIS
"NOTE :
- Data Archive » content must be extracted into Internal Storage.
It may take a while as it is a large collection of files.
- Install, launch the APK"
The whole obb part was misleading, just extract the "EGIU" file right into your Internal Storage main directory and then install the APK, finally it will work.
Just 1247 days for figuring that one out...