Final answer:
The true statement concerning the growth of services is that services now constitute the largest economic sector in postindustrial societies. The other options regarding the stability of manufacturing jobs and the productivity of manufacturing employees are not supported by the evidence provided.
Step-by-step explanation:
Among the options presented concerning the growth of services, statement (a) 'Services now constitute the largest economic sector in postindustrial societies' is true. The evidence shows that the service sector has seen a dramatic increase over the last several decades, becoming the largest component of GDP in postindustrial economies like the United States. This growth is attributed to the rise of the information age and a shift away from manufacturing-based jobs. However, statement (b) 'The number of people employed in manufacturing has more or less held steady since 1950' is not true. Manufacturing jobs peaked in the late 1970s and have since declined by more than a third. Additionally, statement (c) 'Each manufacturing employee now produces about 20 times more than in 1950' might imply increased productivity, but there's no specific evidence provided to support this exact figure, although productivity has generally increased due to technological advancements. Therefore, statement (d) 'All of the above are true' is incorrect, and the correct choice is (a), considering the factual evidence presented.