胚胎期出现造血功能最早的是( )

A．卵黄囊

B．肝脏

C．脾脏

D．骨髓

The relational database model requires the data be (110) through programs that don’t rely on the position of the data in the database. This is in direct (111) to the other database mode, where the program has to follow a series of pointers to the data it seeks. A program (112) a relational database simply asks for the data it seeks; the DBMS performs the necessary searches and (113) the information. The (114) on how the search is done are specific to the DBMS and vary from product to product.

A．erases

B．provides

C．proves

D．values