Make the following complex sentences shorter with the use of the Infinitive.
Model: The work which is to be done is of great importance. – The work to be done is of great importance.
1. The plan will be discussed at the conference which is to be held in May.
2. The question which is to be discussed at the conference is very important.
3. The engine which is to be used on this locomotive is of a new design.
4. The metro line which will link two districts of the city is being built.
