A:otherwise
B:beside
C:however
D:therefore
钉 ____ ____ ____ ____
弹 ____ ____ ____ ____
扎 ____ ____ ____ ____
还 ____ ____ ____ ____
拧 ____ ____ ____ ____
削 ____ ____ ____ ____
一个基因表达载体的构建不包括( )