Resolved questions
noun +of +noun, noun+'s+ noun, or noun+noun? is there any rule?

using a noun(1) describe another noun(2), I know three ways: inserting an 'of' between the two nouns, plus 's after noun(1), and puting noun(1) before noun(2). Such as:

the top of the mountain;
the mountain's top;
the mountain top;

or:

the level of English
the English's level
the English level

Are all of the three forms right?