If induction system screens are used—

1. (a) Each screen must be upstream of the carburetor;
2. (b) No screen may be in any part of the induction system that is the only passage through which air can reach the engine, unless it can be deiced by heated air;
3. (c) No screen may be deiced by alcohol alone; and
4. (d) It must be impossible for fuel to strike any screen.