Explanation:

Let’s break it down:

- First, look at how ‘PAIR’ becomes ‘ZKIR’. The last two letters (“IR”) stay the same. The first two letters “PA” become “ZK”.

- For ‘SAIL’ and ‘ZHOR’: again, last two (“IL”) change to “OR”, first two “SA” turn into “ZH”.

- The trick: it’s not a straightforward alphabetical shift. Instead, the pairs are substituted—first two letters get coded to a certain pair, last two letters to another.

Let’s check what happens with ‘BULK’:

- The last two letters “LK” in ‘PAIR’ and ‘SAIL’ are replaced with “IR” and “OR” respectively. 'LK' may become 'PO' (pattern looks like shift by a certain logic).

- The first two letters “BU” need a similar replacement, which following the same pattern as ‘PA’?‘ZK’ and ‘SA’?‘ZH’, likely becomes “FY”.

So, ‘BULK’ becomes “FYPO”.

- Option 2: FYPO

- Option 1: FPOY (wrong order)

- Option 3: OPYF (wrong order)

- Option 4: YFPO (again, wrong order)

So, the answer is Option 2: FYPO.