The key answer of exercise 4

a)

1. trigger
2. enhance
3. an aspect of
4. sustain
5. deliver
6. success

b)

1. food → trigger rapid weight loss, enhance your capacity to (e.g. function on fewer calories, eat healthily), ignore an aspect of (e.g. nutritional science), sustain long-term motivation (to stick to a diet)
2. learning English → sustain long-term motivation (to study) / sustain Interest in (English), deliver a host of benefits / tangible results (for example, meeting people on holiday), enhance your capacity to (get work / meet people, etc.)
3. discussing an issue → ignore / consider / discuss an aspect of (the issue), deliver a solution (to a problem)

c)

1. long-term motivation / interest
2. memory
3. consider
4. your capacity to
5. success
6. deliver