A Sandal.

It has sticking strips to make them fit for our feet. If you bind them only you can start walking or other wise it comes out.

Cosmology is the scientific study of the large scale properties of the universe as a whole. It endeavors to use the scientific method to understand the origin, evolution and ultimate fate of the entire Universe.

Depending on the outcome of the observations, the theories will need to be abandoned, revised or extended to accommodate the data. The prevailing theory about the origin and evolution of our Universe is the so-called Big Bang theory.

A standing wave also known as a stationary wave, is a wave in which its peaks or any other point on the wave do not move spatially.

This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions. The most common cause of standing waves is the phenomenon of resonance, in which standing waves occur inside a resonator due to interference between waves reflected back and forth at the resonator's resonant frequency.

Hence, standing wave occurs when a wave reflects upon itself.

For undo the action or last action [Ctrl + Z] is used.

We know there are 26 alphabets in English. The 21st letter in the alphabet is 'U'.

We have 5 vowels and 21 consonants.

Vowels :: A, E, I, O, U.

U is not consonant and is a vowel.

Hence, the given statement that 21st letter in the alphabet i.e, U is consonant is a FALSE.