Step 1: Walk iron up the temperature scale mentally.
Instead of memorising the answer directly, imagine slowly heating a bar of pure iron from room temperature all the way to its melting point and note the crystal structure it settles into at each stage.
Step 2: Track the structure changes one boundary at a time.
Below about 912 degrees Celsius iron is alpha ferrite with a body centred cubic structure, between roughly 912 and 1394 degrees Celsius it rearranges into gamma austenite which is face centred cubic, and between 1394 degrees Celsius and the melting point at 1538 degrees Celsius it flips back to a body centred cubic form called delta ferrite.
\[ \text{BCC } (\alpha) \xrightarrow{912^\circ C} \text{FCC } (\gamma) \xrightarrow{1394^\circ C} \text{BCC } (\delta) \]
Step 3: Match this ladder against the options.
Only the option listing BCC alpha, then FCC gamma, then BCC delta reproduces this exact up and down pattern, the other options either put gamma or delta in the wrong crystal system or list the phases out of order.
\[ \boxed{\text{BCC alpha, FCC gamma and BCC delta}} \]