Answer explanations
Why it's right, why the others are wrong
What's on the screen
- 1
The verdict
Correct or incorrect, shown with an icon and a word, next to the objective the question tests.
- 2
Your answer and the correct one
The options appear again in the order you saw them. Your pick and the correct answer are labeled, so the screen reads the same in either theme and to a screen reader.
- 3
Why your answer is wrong
When you miss, this comes first, because it speaks to the exact misunderstanding behind your choice.
- 4
Why the right answer is right
The reasoning in plain language, in 90 words or fewer.
- 5
Why the other options are wrong
A short reason for every remaining option, each labeled with its own text so it makes sense on its own.
- 6
Sources
The title, publisher, and a one-line summary of the evidence, such as an RFC section or a Microsoft Learn page. It opens in your browser.
Incorrect
N10-009 · TroubleshootingUsers on a new VLAN get 169.254.x.x addresses. The DHCP server is on another subnet and already has a scope for the VLAN. What is the MOST likely cause?
The DHCP scope for the new VLAN is exhausted.
Your answer
The router interface for the new VLAN has no DHCP relay configured.
Correct answer
The DHCP scope has the wrong default gateway option.
The DNS server address in the scope is unreachable.
Why your answer is wrong
A brand-new scope with no clients yet hasn't run out of addresses.
Why B is right
A client with no lease broadcasts DHCPDISCOVER on its own subnet. Routers don't forward broadcasts, so a server on another subnet only hears it through a relay agent. With no lease, the client falls back to a 169.254/16 link-local address.
Why the other options are wrong
Sources
RFC 2131, section 3.1
IETF · Clients broadcast DHCPDISCOVER locally; relay agents pass it to servers on other subnets.
RFC 3927
IETF · IPv4 link-local addressing uses 169.254/16.
Written for each question, approved with it
Explanations aren't generated while you wait. Each one is written for its question, checked against the cited source, and approved by a human reviewer at the same time as the question itself. What you read is exactly what the reviewer signed off on.
Options are shuffled each time you see a question, so explanations never say “option B.” They name the thing instead, like “SSH uses TCP port 22,” and the screen supplies the letters you saw.
Multiple-response questions mark each option as correct and picked, correct but missed, wrong and picked, or wrong and not picked, and the ones you got wrong are explained first.
Simulations use the same screen. Each grading rule shows whether you passed it, what the setting does, and the source. See the PBQ lab.
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Every question you can answer for free, including the mini mock exam, daily drill questions, free simulations, and the generators, gets the complete explanation screen. Paying unlocks more questions, not better answers.
If an explanation isn't clear, you can ask for it a different way (simpler, by analogy, or step by step), grounded only in that question's sources, or rate it and report a problem. Reports go straight into the review queue.
Common questions
- Do I see explanations when I answer correctly?
- Yes. A correct answer gets the full screen too. The section on why the other options are wrong starts collapsed, and it's often where a lucky guess turns into real understanding.
- When do explanations appear in a mock exam?
- Not during the exam, which stays realistic. After you submit, every question in the results opens to the explanation screen, and you can step through only the ones you missed.
- Where do the sources come from?
- Standards bodies and registries such as the IETF, IANA, and NIST, and vendor documentation such as Microsoft Learn and Apple Support. Other prep sites, Wikipedia, forums, and videos are never used as evidence.