What are two reasons for this problem?

I cannot figure out what the author is trying to see if we know. The FTP ALG being disabled would not stop you from “connect”ing, the ALG would prevent the data portion of the FTP from connecting. The question does not say “file transfers fail”, it says you cannot connect to the FTP server.

If it did say file transfers are failing, then A + B would be plausible because you can make active FTP work with ALG disabled by allowing traffic in the reverse direction albeit the security implications.

For this reason A + B is tempting despite the fact the control connection would actually “connect” which makes A wrong outright imo.

However to answer the question most accurately based on the selections given, certainly the FTP server not having it’s default route, and the SRX not having a route to the FTP server assuming it’s not directly connected would break the connection.

In situations like this I go with what I feel is the best answer and not bet against the authors competence. So I’d go with C,D