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【单选题】
在家狗中，基因型A_B_为黑色，aaB_赤褐色，A_bb红色，aabb柠檬色。一个黑狗与柠檬色狗交配，生一柠檬色小狗。如果这只黑狗与另一只基因型相同的狗交配，则子代中红色和赤褐色的比例是 [ ]A.
9：16
B.
1：1
C.
3：1
D.
9：1
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皮皮学刷刷变学霸
举一反三
【单选题】—Where________? —He has left a (n) ________ saying that he has something important to do. [ ]
A.
has Tom gone; message
B.
has Tom been; note
C.
will Tom go; word
D.
did Tom go; excuse
【单选题】Why didn't he go to see the doctor immediately?
A.
He has no time during weekdays.
B.
He has no time during weekends.
C.
The symptoms disappear on weekends.
D.
Both A and
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