The convention of Biological Diversity (CBD) was first opened for signature during.

The correct option is Earth Summit.

Step-by-step Explanation:
The Convention on Biological Diversity (CBD) is a landmark multilateral treaty with three main goals: the conservation of biological diversity, the sustainable use of its components, and the fair and equitable sharing of benefits arising from genetic resources.

The CBD was opened for signature on 5 June 1992 at the United Nations Conference on Environment and Development (UNCED), which is popularly known as the Earth Summit, held in Rio de Janeiro, Brazil. It received 168 signatures during this period and subsequently entered into force on 29 December 1993.

Understanding the other options:
• Conference on human environment: This conference was held in Stockholm, Sweden, in 1972. While it laid the foundation for modern international environmental politics and led to the creation of the United Nations Environment Programme (UNEP), the CBD was not established here.
• Montreal Protocol: Adopted in 1987, this is an international treaty designed specifically to protect the ozone layer by phasing out the production of ozone-depleting substances.
• COP1: This refers to the first Conference of the Parties. The COP1 for the CBD took place in Nassau, Bahamas, in late 1994, which was well after the convention had already been opened for signature at the Earth Summit in 1992.