鼻及鼻窦内翻性 * * 状瘤多次手术后易产生恶性变，恶变率为（）。 A.1% B.7% C

I soon found that the work I was doing had already been done by someone else.________, I was

wasting my time. [ ]

A. In other words   

B. In a word

C. First of all  

D. Believe it or not

___________his homework, the boy went out to play.

A．Doing

B．Done

C．Having done

D．To do

下列变化中，属于还原反应的是

A．Cl^－→Cl₂

B．FeCl₂→FeCl₃

C．C→CO₂

D．KMnO₄→MnO₂

观察下列各式9－1=8，16－4=12，25－9=16，36－16=20…，这些等式反映了正整数间的某种规律，设n表示正整数，用关于n的等式表示为            .

组成20种氨基酸三联体密码的碱基是A、T、G、C。