Environmental issues, and particularly climate change, were not at the top of the UN agenda during the 1950s and 1960s. In fact, it was not until late 1960s that environmental issues received serious attention by any major UN organ. In 1969, deliberations about acquiring a balance on all elements of social and economic development, particularly in developing countries, were held in ECOSOC and in the General Assembly. Subsequently, the Commission for Social Development submitted a draft Declaration on Social Progress and Development, which was adopted by the General Assembly in 1969. This was the first time an international instrument provided clear guidelines for not only social policies but also the integration of economic and social action toward improving the social environment and the well-being of the individual.

The correct answer is D.