control *oneself / <<ascetic>> deny *oneself / restrain *oneself / exercise self-denial

apply *oneself to / work diligently / work hard / exert *oneself in / busy *oneself with [one's work]

nod off / nod in a doze / nodding / doze off / nod

nod [one's approval] / give a nod / nod

National Foundation Day / National Foundation Day of China

(of the way in which something is done) on the sly / (of the way in which something is done) in secret / (of the way in which something is done) secretly / (of the way in which something is done) quietly / (of the way in which something is done) without letting anyone know

secretly

secretly

secretly

quiet / underground / private / in secret / stealthily / secretly / under wraps / tacitly / stealthy / privately / secret / tacit / confidentially / quietly / confidential / under cover