Refer to figure. 
Jet lag or circadian dysrhythmia is a disturbance that occurs to the human body due to crossing time zones. This disturbance is related to your sleeping patterns. The human body has its own 'internal clock' that organizes its rhythmic functions. This clock signals the body to wake up in the morning or fall asleep at night, regulates the body temperature throughout the day and signals hormone production. This internal clock follows a 24-hour cycle in constant environment. Otherwise (e.g. while travelling), the cycle becomes 25 hours. When you travel across time zones, this clock becomes 'desynchronized' and needs time to adjust to the new environment. During this adjustment you might experience fatigue and desire to sleep during the daytime. Let's see the difference between a flight towards the west and east respectively:

• Travelling Westwards: London – New York 
  New York is 5 hours behind London, so noon occurs 5 hours later. This means that an aircrew will experience a 29 hour day. However, our free-running body clock is 25 hours, which means that the crew will suffer from 4 hours jet lag.
• Travelling Eastwards: New York – London 
  London is 5 hours ahead of New York so noon occurs 5 hours earlier. This means that an aircrew will experience a 19 hour day. However, our free-running body clock is 25 hours which means that the crew will suffer from 6 hours jet leg.

Jet Lag after travelling eastwards is more than westwards. The body adjusts about 90 minutes for each day.

Let's examine the given options:

The natural clock is affected more than when flying in a westerly direction. → CORRECT. Jet Lag after travelling eastwards is more than westwards.

The natural clock is affected less than when flying in a westerly direction. → INCORRECT. Jet Lag after travelling eastwards is more than westwards.

The natural clock adjusts at the same rate regardless of direction. → INCORRECT. Jet Lag after travelling eastwards is more than westwards.

The natural clock is unaffected if the flight occurs during daylight hours. → INCORRECT. Jet Lag occurs when crossing time zones during day and night.