What characteristics of a point on the string will you use to find the location of the antinode?
A) displacement
B) velocity
C) wavelength
D) time

Hint
In a standing wave, antinodes are the points which have maximum displacement or oscillating with maximum amplitude. The movement of a string can form a standing wave. When two waves having the same amplitude and frequency, propagating in opposite directions of each other combine, then a standing wave is formed.

Complete step by step answer
Antinodes are formed in the Standing Wave and the movement of a string can form a standing wave. So, let us first discuss a standing wave.
When two waves having the same amplitude and frequency, propagating in opposite directions of each other combine, then a standing wave is formed.
Now, let us discuss the nodes and antinodes.
In a standing wave, nodes are the points which have zero amplitude whereas antinodes are the points which have maximum displacement or oscillating with maximum amplitude.
Node is also called as the point at which destructive interference takes place whereas antinode is the point at which constructive interference takes place.
Therefore, we can find the location of an antinode by using the characteristic displacement.
Hence, option (A) is correct.

Note
The actual movement of a standing wave cannot be observed by our naked eyes. The adjacent points in a standing wave remain in phase and hence there is no energy transfer from one point to the next point. The process of formation of standing waves is also called superposition of travelling waves (in opposite direction) having the same amplitude and frequency.