We also report some results from new experiments suggested by the reviewers

We thank all four reviewers for their constructive comments. We respond to each reviewer's comments separately below. We also report some results from new experiments suggested by the reviewers. This idea is illustrated in Figure 2 in the paper. Second, we followed the reviewer's suggestion and developed a temporal version of MoCo as a new baseline: MoCo-Img: 46.6% in the labeled S dataset).