In the description of embodiments of the present disclosure, unless otherwise explicitly specified or defined, the terms “connect”, “fixed connection”, “install” and “assemble” are to be understood broadly, for example, a connection may be a fixed connection, or a detachable connection, or an be integral connection. The terms “install”, “connect” and “fixed connection” may refer to a direct connection, or an indirect connection through an intermediate medium, or an internal connection between two elements. Those of ordinary skills in the art can understand the specific meanings of the above mentioned terms in the present disclosure according to specific context.