Explanation:

The Cray-1, designed by Seymour Cray and released by Cray Research, is widely recognized as one of the first and most successful supercomputers. It was first delivered to the Los Alamos National Laboratory in 1976. This machine revolutionized high-performance computing with its innovative vector processing architecture. While other powerful computers existed before, the Cray-1 set a new standard for supercomputing. Therefore, the year 1976 ($ \text{b} $) marks the development and delivery of this landmark supercomputer. The other years listed are either too early or too late for this specific milestone.