估算29×31,想:29≈______,31≈______,29×31≈______.
因为29≈30,31≈30,
所以29×31≈30×30=900.
故答案为:900.
27.As Senior 3 students, it is important to________a good state of mind.
A.keep up
B.stick with
C.attend to
D.tie up
下列哪种疾病与激素分泌异常无关 [ ]
A.侏儒症
B.巨人症
C.夜盲症
D.糖尿病