ynchronizing devices are designed to prevent gear clash when shifting intoa.Second and highb.First and secondc.First and reversed.Reverse and Second

Synchronizing devices are designed to prevent gear clash when shifting gears in a vehicle. They work by matching the speed of the gear and the shaft before allowing them to engage, thus preventing any clashing or grinding.

Here's a breakdown of when they are used:

a. Second and high: Synchronizers are used when shifting between these gears to ensure a smooth transition and prevent gear clash.

b. First and second: Similarly, synchronizers are used when shifting between these gears. This is especially important as shifting from first to second often involves a significant change in gear ratios.

c. First and reverse: Synchronizers are typically not used when shifting into reverse. This is because reverse is usually engaged from a standstill, so there's no need to match gear speeds. However, some modern vehicles do use synchronizers for reverse to make it easier to engage.

d. Reverse and Second: As with first and reverse, synchronizers are typically not used when shifting from reverse to second as these shifts are usually made from a standstill.

So, to answer your question, synchronizing devices are designed to prevent gear clash when shifting into second and high, and first and second. They are typically not used when shifting into first and reverse, or reverse and second.