Let R and S be the relation respection respectively：

Relation R:A B C Relation S:B C D

1 2 3 2 3 4

6 7 8 2 3 5

9 7 8 7 8 1

The number of tuples that the result of the expression R∞S(Here if natural join of relations R and S) is (69) ．(69)

A．1

B．4

C．7

D．10

[单选题]Let R and S be the relation respectively: Relation R: A B C Relation S: B C D 1 2 3 2 3 4 6 7 8 2 3 5 The number of tuplesthat the result of the expression R ∞ S (Here is the natural join of relations R and S) isA．3B．4C．6D．9

[单选题]Let R and S be the following relations：A．3B．4C．5D．6

[单选题]F．or relation R where primary key contains multiple, no non-key attribute should be functionally dependent on a part of the primary key.This relation R is at least inA．1NFB．2NFC．3NFD．BCNF

[单选题]Suppose we have the relation schema R(A,B,C,D)with functional dependencies;F{A→B,B→C,C→D,D→A},then R(A,B,C,D)at least is inA．1NFB．2NFC．3NFD．BCNF

[单选题]Suppose we have the relation schema R(A，B，C，D)with functional dependencies；F{A→B，B→C，C→D，D→A}，then R(A，B，C，D．at least is in (73) ．(73) A．1NFB．2NFC．3NFD．BCNF

[单选题]F．or relation R where primary key contains multiple attributes,no non-key attribute should be functionally dependent on a part of the primary key. This relation R is at least inA． 1NFB．2NFC．3NFD．BCNF

[单选题]C．onsider a relation R ( A，B，C，D ) with the following dependencies： AB ? C, CD ? E, DE ?B.A．ABB．ABCC．ABDD．ABE

[单选题]Let's ______.A.play footballB.play a footballC.play the footballD.play foot

[单选题]（ ）–It’s raining heavily.Let’s stand under that big tree.–__________.It’s very dangerous to do so in such weather.A．We don’t have toB．Let’s goC．All rightD．We’d better not

[单选题]Let’s ___ play in the street . Father tells me ____ do so.A． not to ….. not toB． not …not toC． don’t , to notD． not to …don’t