S1: To a foreign learner, English pronunciation presents the greatest difficulty.
S6: But knowledge of Phonetics will help a great deal in learning correct English pronunciation.
P: Words are spelled in one way and pronounced in another.
Q: For instance 'u' has different pronunciation in 'but', 'put', 'build' and 'bury'.
R: The English language is notoriously un-phonetic.
S: The same letters give different sounds in different words.

The proper sequence should be :
a. PRSQ
b. QSPR
c. SPQR
d. RPSQ

Hint: The sentences tell a story. The story has to be in the right order. Try to rearrange it in the order that makes the most sense.

Complete answer: The question tells us to arrange the sentences with the
preexistence of the first concrete sentence. This means that we have a starting point. So, we can take hints from the first sentence.
The first sentence begins by telling us that learning English is a difficult task for a foreigner. This means that the next sentence should prove the first sentence.
This is done by sentence Q. It provides an example of the first statement made. Now, we need further information about sentence Q, which is done by sentence S.
Then, we need a sentence that introduces a newer topic. This is done by sentence P. Then, we need a sentence that concludes the paragraph. The only sentence left is sentence R.

So, we understand which order we need. Now, let’s look at the given options:
a. PRSQ - This order places sentence ‘P’ as the first sentence, which is not correct. This is not the order that is required. This is not the required answer. So, this is an incorrect
option.
b. QSPR - This order places sentence ‘Q’ as the first sentence, which is correct. This is
the exact order that is required. This is the required answer. So, this is the correct option.
c. SPQR - This order places sentence ‘S’ as the first sentence, which is not correct. This is
not the order that is required. This is not the required answer. So, this is an incorrect
option.
d. RPSQ - This order places sentence ‘R’ as the first sentence, which is not correct. This is
not the order that is required. This is not the required answer. So, this is an incorrect
Option.
Therefore, option b is the correct answer.

Note: Make sure that each sentence aligns with the sentences that come before and after. That will help you to choose the order correctly.