The is the lengthwise yarns which are arranged in right angles next to each other.
a. weft
c. weave
b. warp
d. grain

The warp is the longitudinal yarns positioned beside each other at right angles.

Explanation:

The warp is the longitudinal yarns positioned beside each other at right angles.

The fiber that is put in a woven fabric's in a longitudinal direction is termed  as warp yarn. Warp thread is used to create a frame for weaving. The fiber (yarn) used by the warp beam to cross interlace is termed as weft yarn. Warp yarn number is finer than the number of weft yarns

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.