Select the most more appropriate option to fill in the blank.

_______ he is a hard worker, his quality of work is not of a desirable level.

Although

The most appropriate option to fill in the blank is Although.

The sentence "Although he is a hard worker, his quality of work is not of a desirable level" means that he works hard, but his work is not of a high quality. The word "although" is the most appropriate word to use in the blank because it accurately reflects the fact that there is a contrast between the two clauses of the sentence.

The other options are not as appropriate.

• The word "despite" is also used to talk about a contrast, but it is more commonly used when the contrast is negative. In this case, the contrast is not negative, so "although" is the better choice.
• The word "since" is used to talk about a reason or cause. In this case, the reason for the poor quality of work is not being stated, so "since" is not the best choice.
• The word "because" is also used to talk about a reason or cause. However, it is more commonly used when the reason is obvious or well-known. In this case, the reason for the poor quality of work is not obvious, so "because" is not the best choice.