1. 如图,在$□ ABCD$中,一定正确的是(

A. $AD = CD$ B. $AC = BD$ C. $AB = CD$ D. $CD = BC$
C
)A. $AD = CD$ B. $AC = BD$ C. $AB = CD$ D. $CD = BC$
答案:
C
2. 如图,在$□ ABCD$中,$AC\perp AB于点A$,若$\angle ACB = 30^{\circ}$,则$\angle D$的度数为(

A. $60^{\circ}$ B. $50^{\circ}$ C. $45^{\circ}$ D. $40^{\circ}$
A
)A. $60^{\circ}$ B. $50^{\circ}$ C. $45^{\circ}$ D. $40^{\circ}$
答案:
A
3. 如图,$□ ABCD的对角线AC$、$BD交于点O$,下列结论一定成立的是(

A. $OA = OB$ B. $OA\perp OB$ C. $OA = OC$ D. $\angle OBA = \angle OBC$
C
)A. $OA = OB$ B. $OA\perp OB$ C. $OA = OC$ D. $\angle OBA = \angle OBC$
答案:
C
4. 如图,$\triangle DBF和\triangle EFC都可以由\triangle ADE$平移得到,则图中共有______

3
个平行四边形.
答案:
3
5. 如图,$□ ABCD的对角线AC与BD相交于点O$,$\angle BAC = 90^{\circ}$,$AC = 6$,$BD = 10$,则$CD$的长为______

4
.
答案:
4
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