SOURCE : GMAC Bulletin 2008
Test-Preparation courses and tutorials are also available from individuals and companies not associated with GMAC, many of which are Web-based.
As per GMAT english, is this sentence completely right ?? in 'Many of which' - 'Which' logically refers to Test-prep courses and tutorials- a phrase which is totally distant from the which ... It could incorrectly refer to individuals and companies ...
Kindly clarify
PS : I hope quoting the GMAC bulletin is not illegal !!!