The sentence can be completed as follows:
The wavelength of an electromagnetic waves is the spatial distance between two successive troughs.
Note that the wavelength of a wave can also measured as the spatial distance between two successive crests of the wave. Also note that the second part of the sentence ("also known as the period") is not true, because period is another thing (in fact, the period is the time interval between two successive troughs).
Answer:
The new force becomes 4 times the initial force.
Explanation:
The force of attraction or repulsion is given by the relation as follows :

Where
d is the distance between the interacting charges
F is inversely proportional to the distance between charges.
If the distance is halved, d'=(d/2), new force is given by :

So, the new force becomes 4 times the initial force.
Yep. he discovered that coastline from south america and africa fit together like a puzzle, which later became a part of the continential drift theory
Keep cool by being active at night, whereas some other desert animals get away from the sun's heat by digging underground burrows.
//////Correct answer is C.///////