West Bengal Chief Minister Mamata Banerjee on Wednesday demanded an investigation into the opposition parties' assets, alleging that the lion's share of the income of the Congress, BJP and CPI-M were from unknown sources."The sources of 82.5 percent of the Congress's income, 73 percent of the BJP's income and 53 percent of the CPI-M's income are unknown. It should be investigated. From where is this money coming in," Banerjee said at an election rally in Dum Dum of North 24 Parganas district.The Trinamool Congress supremo attacked the opposition for its continued slander campaign and mocked the "unholy nexus" of the CPI-M and the Congress.On Tuesday too, at an election meeting in Jagatballabhpur of Howrah district, Banerjee had spoken about the "unknown sources" of income, and said the opposition should not "dare to point fingers at Trinamool".She had said the opposition's only agenda was to "abuse" her and "insult" Bengal.