是定语从句.因为先行词是the black cat在从句中做saw的宾语.关系代词that代替先行词在从句中做宾语.从句意思：这就是我上次看到的那只猫.如果是强调句.应该是这样的：It was the black cat that I saw last time.强...去掉后变为 I saw the black cat last time. 不是也通吗it was the black cat that I saw last time.去掉it was ,,that后变为 the black cat I saw last time.强调句前后时态要一致。定语从句可以不一致具体看语境