Read these statements about pent-2-en-4-ynal, $\text{HC}\equiv\text{C}-\text{CH}=\text{CH}-\text{CHO}$. (i) One molecule has $9$ σ bonds and $4$ π bonds. (ii) Three carbon atoms are $sp^2$ hybridised and two are $sp$. (iii) The single bond between C-3 and C-4 is made by an $sp^2$ orbital of C-3 and an $sp$ orbital of C-4. (iv) The bond angle at C-4, between C-3 and C-5, is about $120^\circ$. (v) Its $\equiv\text{C}-\text{H}$ bond is longer than the $\text{C}-\text{H}$ bond of its CHO group. How many of the statements above are correct?