Choose the on which best expresses the meaning of
FLOUNDER
a) run
b) fluctuate
c) jump
d) stumble

Hint:Synonyms are words or phrases that mean exactly or nearly the same as another word or phrase. For example- ‘sad’ and ‘depressed’.
Two words that can be interchanged in a context are said to be synonymous relative to that context.

Complete answer:
In the given question, the word ‘flounder’ refers to walking with great difficulty.
Let us analyze the options given to us in this question:
Option (a.), 'run', refers to moving fast by using one's feet, with one foot off the ground at any given time.
Therefore, option (a.) is incorrect as its meaning is not synonymous to that of the given word ‘flounder’.

Option (b.), ‘fluctuate', refers to being unstable.
Therefore, option (b.) is incorrect as its meaning is not synonymous to that of the given word ‘flounder’.

Option (c.), ‘jump', refers to moving forward by leaps and bounds.
Therefore, option (c.) is incorrect as its meaning is not synonymous to that of the given word ‘flounder’.

Option (d.), ‘stumble', refers to walking unsteadily
Therefore, option (d.) is correct as its meaning is synonymous to that of the given word ‘flounder’.

Note: If you don’t know the definition of the given word and have only used it in some given context previously, then use the given word in a sentence. Substitute the given word with each word in the options and choose the word which does not conflict with the context provided by the given word.