Received: 27 September 2018
Accepted: 30 January 2019
First Online: 21 February 2019
Ethics approval and consent to participate
: All participants involved were informed of the purpose of this study and a written consent was obtained from their parents or legal guardians. This study has been approved by the Ethics Committee of Beira Interior University (CE-FCS-2012-027).
: Not applicable.
: The authors declare that they have no competing interests.
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