First of all, let's look at definitions for IPS and IDS:
An intrusion detection system (IDS) is a device or software application that monitors a network or systems for malicious activity or policy violations. Any detected activity or violation is typically reported either to an administrator or collected centrally using a security information and event management (SIEM) system.
Intrusion prevention systems (IPS) [...] are network security appliances that monitor network or system activities for malicious activity. The main functions of intrusion prevention systems are to identify malicious activity, log information about this activity, report it and attempt to block or stop it.
Intrusion prevention systems are considered extensions of intrusion detection systems because they both monitor network traffic and/or system activities for malicious activity. The main differences are, unlike [IDS], [IPS] are placed in-line and are able to actively prevent or block intrusions that are detected. IPS can take such actions as sending an alarm, dropping detected malicious packets, resetting a connection or blocking traffic from the offending IP address.
Now let's look at the question and the given answers:
Which of the following statements are true? (Select all that apply)
a.- An IDS deals with malicious traffic that the firewall missed.
As we just learned, an IDS is only used for monitoring and not for "dealing with" (whatever that means exactly). It is fair to say that IDS is not actively involved in blocking or filtering such traffic, so "dealing with" is probably: FALSE.
As Georgios pointed out, "dealing with" could also be interpreted less actively, so this might be TRUE. English is not my first language, so other comments are welcome.
b.- An IPS is on the boundary of the trusted inside and the untrusted
I wouldn't say so, but you could argue it that way. Typically the IPS sits behind the boundary - this is where the firewall would be - to lower the load of traffic the IPS has to analyze. The firewall filters out most of the easy-to-detect unwanted traffic, the IPS takes care of the more sophisticated stuff.
In my view: FALSE.
c.- A network-based firewall protects hosts from malicious traffic
originating on their same network.
Nope. A network-based firewall protects hosts inside a network from malicious traffic that originates from the internet or any other network that sends traffic to these hosts. A host-based firewall protects a host (if set up correctly) from all sorts of traffic, irrelevant where it comes from. This would be a software that is installed on a machine, like Windows firewall.
d.- An IPS protects hosts from malicious traffic originating on their
Helloooo, there it is. This is a correct statement. BUT, an IPS does more than that. See (at least) wikipedia article for more information on that.