Final answer:
The correct statement is that you can use the tachometer to tell you when to shift, which helps ensure smooth acceleration and prevent engine overstress.
Step-by-step explanation:
The true statement about double-clutching and shifting is that C. You can use the tachometer to tell you when to shift. Double-clutching is a technique used primarily in vehicles with unsynchronized manual transmissions to match the speeds of the input and output shafts of the gearbox. This technique is not dependent on the weight of the load a vehicle is carrying.
Additionally, missing a gear while shifting does not necessitate bringing the vehicle to a complete stop; you can usually attempt to shift again. Using a tachometer is common practice to determine the engine speed and decide the optimal time to shift gears to ensure smooth acceleration and to avoid overstressing the engine.
The correct statement about double-clutching and shifting is B. Double-clutching should be used only with a heavy load.
Double-clutching is a driving technique used when shifting gears to match the RPM of the engine and the RPM of the transmission. It involves depressing the clutch twice during the shifting process. Double-clutching is particularly useful when there is a heavy load because it helps to synchronize the gears and reduce the strain on the transmission.
The tachometer in the car shows the engine's RPM and can help indicate when to shift gears, but it is not the only indicator. Other factors such as engine sound, road conditions, and speed should also be considered when deciding when to shift.