The correct answer is B) recessed tie down points. The landing deck of a MODU (Mobile Offshore Drilling Unit) must be fitted with recessed tie down points to enable the safe tying down of a helicopter. These recessed points provide secure attachment points for the helicopter's tiedown lines, ensuring the aircraft is firmly secured to the deck during landing, takeoff, and while parked. This is a regulatory requirement to maintain the stability and safety of the helicopter operations on the MODU. The other options are incorrect because: A) hydraulically lifted bitts are not required for helicopter tie-down, C) air tuggers are used for mooring ships, not securing helicopters, and D) fixed cleats, while useful for other purposes, do not provide the same level of security and integration into the landing deck design as recessed tie down points.