Answer:
The given question is incomplete; options are missing.  
The missing options are:
A. valid because this conclusion is believable.
B. valid because this is indeed a valid syllogism and the logic is apparent.  
C. invalid because this syllogism does not involve a pragmatic reasoning schema.  
D. invalid because of the influence of the atmosphere effect.  
The correct answer is option A.  
Explanation:
Syllogism is a rhetorical device used to draw a conclusion about certain arguments(premise). It is a form of logical reasoning. 
A syllogism can be divided into three parts: 
- Minor premise 
- Major Premise 
- Conclusion 
In the given case, the major premise is <em>"some tired people are irritable" </em>because it is stating a fact;<em> "all of the students are tired"</em> is a minor premise that is specifying a statement, and <em>"some of the students are irritable"</em> is a conclusion drawn from the major and minor premise. 
This syllogism will be considered valid because the conclusion is believable.