Let R and S be the following relations：

A．3

B．4

C．5

D．6

[单选题]What operation on relations R and S produces the relation shown below?A．UnionB．DifferenceC．IntersectionD．Division

[单选题]Let R and S be the relation respection respectively：Relation R:A B C Relation S:B C D1 2 3 2 3 46 7 8 2 3 59 7 8 7 8 1The number of tuples that the result of the expression R∞S(Here if natural join of relations R and S) is (69) ．(69) A．1B．4C．7D．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]Generally speaking, the syntactic relations include three basic types. Whic

Let’s keep in ________.Here is my card. Let’s keep in ________. A. re

Let’s keep in _______ .A. friendshipB. connectionC. relationD. touch

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

Lets keep in _______.A. touchB. relationC. connectionD. friendship

[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