My normal advice for task 2 introductions is this: write two sentences - one to introduce the essay topic, and one to give a basic answer to the question. But what should you put in the second sentence (basic answer) if the question doesn't ask for your opinion?
Here are two example questions:
- Many people believe that an effective public transport system is a key component of a modern city. Discuss the advantages and disadvantages of public transport.
- Crime rates tend to be higher in cities than in smaller towns. Explain some possible reasons for this problem, and suggest some solutions.
Here are two sample introductions:
- Officials in many cities are keen to develop efficient public transport systems. While public transport has many benefits, there are also some drawbacks which are worth considering.
- Cities generally experience higher levels of criminality than towns or villages. There are various reasons for this, but measures could be taken to tackle the problem.
Hopefully you can see that it's quite easy to write an introduction for these types of question. The approach is the same (topic + basic answer) whether the question asks for your opinion or not.