You are maintaining your OLTP database in Oracle10g. You have not set the warning level and critical level threshold values for space usage of the DATA1 tablespace. What will be the impact？（）
A. No warning level or critical level alert will be generated.
B. A warning level alert will never be generated， but a critical level alert will be generated when 97 percent space of the DATA1 tablespace is used.
C. A critical level alert will never be generated， but a warning level alert will be generated when 85 percent space of the DATA1 tablespace is used.
D. A warning level alert will be generated at 85 percent space usage of the DATA1 tablespace， and a critical level alert is generated at 97 percent space usage of the DATA1 tablespace.
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