The acceleration of an object is directly proportional to the net force acting on it. Zero net force means zero acceleration.
If I remember correctly (from my studies long time ago) the layers are from the outer to the center:
SiAl : Silicon-Aluminum
SiMa : Silicon-Magnesium (although should be Mg)
NiFe : Nickel-Iron
The SiMa layer should have the lightest elements (Magnesium is lighter than Aluminum)
Liters
Grams
Degrees Celsius
The other answer choices are from the imperial system
"F=Vector Sum Of The Two Forces" Is the answer.