1One of the major topics to be investigated in …is…
2There is a growing body of literature that recognizes..
3Recently, the problem of X has aroused people’s concern
1A challenging problem which arises in this domain is…
2Research on…has a long tradition
背靠大树好乘凉，a long tradition意味着有很多大佬的文献可以参考~
3A well-known problem with…is that it does not take into account the…