将下列透视术语的代表符号填在括号内。
主视线( )。
参考答案：so
The world economy has improved ________ since the end of last year，but major problems and challenges are not fully solved.
A．somehow
B．somewhat
C．anyhow
D．meanwhile
流感病毒发生变异的形式有（）
A.抗原转移、抗原漂移
B.抗原转移、抗原转换
C.抗原替换、抗原转换
D.抗原替换、抗原转移
E.抗原转换、抗原漂移
