$\underset{I}{\underline{\text{All engineering students}}}\; \underset{II}{\underline{\text{should learn mechanics,}}} \;\underset{III}{\underline{\text{mathematics and}}}\; \underset{IV}{\underline{\text{how to do computation.}}}$

Which of the above underlined parts of the sentence is not appropriate?

1. I
2. II
3. III
4. IV