A loose timing belt will cause a flapping sound near the front of the engine.

Piston slap is a knock heard at the side of the engine which is louder when the engine is cold and goes away or is reduced when the engine reaches operating temperature.

The purpose for disconnecting the fuel injection and ignition systems is SAFETY related. Reading accuracy is very important but not what was asked.

Both technicians are correct. Tech A is right because engine RPM (Revolutions Per Minute) is an indicator of when that cylinder is contributing to the engine power and if it is balanced. You note the RPM before and during the test so when the cylinder is shorted out you can tell if it changes. Tech B is right because when the engine speed (RPM) does not drop or change, then that cylinder is not having an effect on engine operation or balance. 

A valve seal is shown in the picture.

Technician A is a correct. A closed coil end of a valve spring should go against the cylinder head. Technician B is wrong because all valve springs do not use shims to control assembled height. It is also wrong because it should state assembled height.

You must check the specific OEM procedure for adjusting valves either hot or cold.

Grinding the valve stems will have to be done because the distance has been reduced between the rocker and the pushrod, so you grind the valve stem to compensate.

Rod bearing noise is a thumping noise or knock at the side of the engine block that is louder when the engine is hot and goes away when the affected cylinder is shorted out. A is wrong because main bearing noise is constant and cannot be shorted out.  A main bearing noise is generally deeper sounding than a rod bearing. Also, a main bearing makes an evenly spaced single knock while a rod bearing generally makes a double knock.  B is wrong. A wrist pin noise can be diagnosed by disconnecting spark plug wires one at a time. Should the noise in the engine immediately double in frequency, then it's a wrist pin. Should the noise merely diminish a bit, then probably a rod knock caused by a loose bearing.  D is wrong because piston slap noise disappears once the engine is warm. Piston slap could be caused by the piston skirt deforming under stress.

A bad rod bearing will make a knocking sound with changes in RPM and disappear when the cylinder is shorted out.

Both technicians are correct. Antifreeze or engine coolant contains corrosion inhibitor that wears out over time, so this is the reason it is recommended that the coolant be replaced and the system flushed at a service interval.  The freeze protection of the coolant never changes.

Distilled water is the least likely required in a cooling system because it has no effect on the cooling ability of the solution.  Distilled water is not required in a cooling system. It is used with battery electrolyte.

The ECM has a stored DTC P1121 (Electric Throttle Control Actuator). When the malfunction is detected, ECM enters fail-safe mode and the MIL lights up. While the engine is in fail-safe mode and malfunction A of DTC P1121 is detected, the engine speed will not rise more than 2,000 RPM and thus cause a low power complaint. The ECM controls the electric throttle actuator by regulating the throttle opening around the idle position.

Technician B is correct because problems with the fuel/air burning (called fuel propagation) will show up within the spark line. Technician A is wrong because the voltage required maintaining spark is referred to as the spark line and the duration of the spark line is based on total secondary circuit resistance (not primary circuit resistance) and coil voltage available. A typical firing voltage for a DI system is 8-10 kilovolts (kv). The spark line, which indicates the amount of time current flows across the spark plug gap, should also be smooth and level. Normal current flow usually lasts 1.2-2 milliseconds. Short or uneven spark lines, like high-firing voltages, indicate high secondary circuit resistance.