см. тж. для этого необходим ; когда это ~ ; нужно ; следует
• There is a need to examine the significance of ...
• If steroids are used it is essential to reduce the dose as soon as possible to 7.5 mg of ...
• The bed needs ( or has ) to be regenerated before it can be used for another 10-min adsorption cycle.
• A very powerful magnetic field is required to ...
• It is essential that the insulation should be well packed.
• Much needs to be done to satisfy these requirements.
• Much remains to be done in this area.
• It takes a very powerful magnetic field to control the path of a particle.