What is the relationship between Lehman Brothers and investment bank in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

Lehman Brothers LEH.N shares fell sharply on Monday on speculation that the investment bank could be bought for $15 a share, a price well below current market levels.

Answer: product_or_material_produced