Funding for this research was provided by:
National Natural Science Foundation of China (81801663, 31630025, and 81571643)
Received: 31 March 2020
Revised: 7 April 2020
Accepted: 24 April 2020
First Online: 13 May 2020
Compliance with ethical standards
: The scientific guarantor of this publication is Wenzhen Zhu.
: The authors declare that they have no conflict of interest.
: No complex statistical methods were necessary for this paper.
: Not applicable.
: Institutional Review Board approval was not required because this publication is a Letter to the Editor.
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