According to Keynes, investment means

Buying out existing factories
Buying shares in the existing firm
Buying an old building
Establishment of new factory

The correct answer is D. Establishment of new factory.

Keynes defined investment as the “expenditure on capital goods”. This includes the construction of new factories, the purchase of new machinery, and the development of new technologies. Investment is essential for economic growth, as it creates new jobs and increases the productive capacity of the economy.

Option A is incorrect because buying out existing factories does not create new capital goods. Option B is incorrect because buying shares in an existing firm does not increase the productive capacity of the economy. Option C is incorrect because buying an old building does not create new capital goods.

In conclusion, the correct answer is D. Establishment of new factory.