这道题不但考察了现在完成时（for two years、two years ago是现在完成时的标志）,还考察了“入团”这个短语的多种形式.
其实我认为这道题以后者考察为主.
毕竟现在完成时就是has/have done的形式,而短语“入团”有join the party或 joined the League、be a League member、be a member of the League……
所以,该填空可以是：
I have been a League member for two years.
I have been a member of the League for two years.
I joined the League two years ago.
I have joined the League for two years.