Can anyone explain why, when using the passive tense to ask a question you sometimes use the construction:
Question word + to be + subject + past participle
e.g.When was Coca-Cola invented?
But sometimes leave to be & past participle together:
e.g. How much Coca-Cola is sold in a day?
The question in your first sentence is 'When?'; in the second, it is 'How much Coca-Cola?'. Compare that with:
How much is Coca-Cola sold for in your country?
In that last sentence, the question is 'How much?' (= at what price?)