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离心泵主要由（）、（）、（）、（）、（）、轴承箱等部件组成。有些泵还有导轮、（）、平衡盘等。

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握手时要（）对方，面带微笑。同时附上“您好”、“欢迎您”、“认识您很高兴”、“好久不见还好吗？”、“下次再见！”等问候和致意语。

You performed an incremental level 0 backup of a database: RMAN > BACKUP INCREMENTAL LEVEL 0 DATABASE; To enable block change tracking after the incremental level 0 backup, you issued this command: SQL > ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE ‘ /mydir/rman_change_track.f’; To perform an incremental level 1 cumulative backup, you issued this command: RMAN> BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE; Which three statements are true?（）

A. Backup change tracking will sometimes reduce I/O performed during cumulative incremental backups.
B. The change tracking file must always be backed up when you perform a full database backup.
C. Block change tracking will always reduce I/O performed during cumulative incremental backups.
D. More than one database block may be read by an incremental backup for a change made to a single block.
E. The incremental level 1 backup that immediately follows the enabling of block change tracking will not read the change tracking file to discover changed blocks.

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地基允许承载力

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Z12V190B型柴油机喷油泵凸轮轴的轴向间隙规定为（）

A. 0.2~0.4mm
B. 0.1~0.3mm
C. 0.3-0.5mm
D. 0.1-0.6mm

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