求解一道数据库的题，用关系代数表达式
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(1) SELECT T.TNAME,T.TITLE
FROM T INNER JOIN C ON T.T=C.T
WHERE C.CNAME="高等数学"
(2) SELECT DLOOKUP("CNAME","C","C='" & SC.C & "'") AS CNAME
FROM S LEFT JOIN SC ON S.S = SC.S
WHERE S.SNAME="ZHANG" AND SC.S Is Null
(3) SELECT C.CNAME, C.C
FROM C INNER JOIN SC ON C.C = SC.C
WHERE SC.S="S2" OR SC.S="S9"
(4) SELECT S, SNAME
FROM S
WHERE AGE>20 AND SEX="男"
FROM T INNER JOIN C ON T.T=C.T
WHERE C.CNAME="高等数学"
(2) SELECT DLOOKUP("CNAME","C","C='" & SC.C & "'") AS CNAME
FROM S LEFT JOIN SC ON S.S = SC.S
WHERE S.SNAME="ZHANG" AND SC.S Is Null
(3) SELECT C.CNAME, C.C
FROM C INNER JOIN SC ON C.C = SC.C
WHERE SC.S="S2" OR SC.S="S9"
(4) SELECT S, SNAME
FROM S
WHERE AGE>20 AND SEX="男"
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