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Choose one answer

1. AThe proportion of REM sleep within each cycle tends to lengthen towards the later cycles of the night
2. BStage N1 sleep comes to dominate every cycle equally from the first cycle through to the last
3. CEach cycle becomes progressively shorter in total duration as the night continues towards waking
4. DSlow-wave sleep increases in each successive cycle, becoming most prominent just before waking
5. EREM sleep is entirely absent from the earliest cycles and only appears in the final cycle before waking