Received: 9 July 2019
Accepted: 5 May 2020
First Online: 15 May 2020
Ethics approval and consent to participate
: The study was approved by the HKU/HA HKW Institutional Review Board (IRB HKU: UW17–348). The age of participants was from 11 to 15 and written consents from the parents were obtained.
: Not applicable.
: The authors declare that they have no competing interests.