Fact 3. Engineer build Houses
- All mammals build houses is $false$ because only some mammals who are engineers as well as humans build houses.
- Engineers are mammals is $false$ since only some engineers (who are humans) are mammals.
- Some humans are not engineers is also $true$ as we can see in fact 2.
$\therefore$ Option B. $Only$ $III$ is the correct answer.
But this answer is not correct.
As mentioned by @Arjun Sir,
In Fact 2 we can say that some human are Engineers but we can't say anything about the remaining humans whether they are engineers or not as it is not mentioned in the question.
So we can't infer that some humans are not engineers as we can have multiple cases for the remaining humans.
Case 1 : The remaining humans are also engineers.
Case 2: The remaining humans are not engineers.
Case 3: Some of the remaining humans are engineers.
Case 4: Some of the remaining humans are not engineers.
Case 5: Some of the remaining humans are engineers and the rest are not engineers.
So, None of the above Statements are correct.