Step 1: Recall hydroboration-oxidation reaction.
Hydroboration-oxidation converts an alkene into an alcohol by anti-Markovnikov addition.
Reagents:
\[
BH_3 \, / \, THF \quad \text{followed by} \quad H_2O_2/NaOH
\]
Step 2: Nature of addition.
OH group attaches to the less substituted carbon of the double bond (anti-Markovnikov rule).
Step 3: Apply to 4-methyl-octene.
Since the alkene has 8 carbon chain with a methyl group at position 4, the product remains an octanol derivative.
So the product formed is 4-methyl octanol.
Final Answer:
\[
\boxed{\text{(A) 4-methyl octanol}}
\]