心電圖上P-R間期代表的時(shí)間是從:A. P波起點(diǎn)至QRS波群起點(diǎn)B. P波終點(diǎn)至QRS波群起點(diǎn)C. P波起點(diǎn)至Q波起點(diǎn)D. P波終點(diǎn)至R波起點(diǎn)