Directions: In this question, the first and the last (correctly ordered) sentences of a passage are numbered 1 and 6. The rest of the passage is split into four parts named B, C, D and E. These four parts are not given in the proper order. Choose the correct combination among the four alternatives given.

1. Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. B. The polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. C. Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients. D. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. E. Unlike sea anemones, corals secrete hard carbonate exoskeletons, which support and protect the coral polyps.
2. Reefs grow best in warm, shallow, clear, sunny and agitated waters.