The question asks to identify the grammatically correct sentence among the given options, focusing on the use of conjunctions and adverbs indicating contrast.

Grammar Focus: Correct Use of 'Although'

The word 'Although' is a subordinating conjunction used to introduce a contrast. When 'Although' begins a sentence, it sets up a contrast between the clause it introduces and the main clause that follows. Standard English grammar dictates that you should not use additional words that also express contrast (like 'still', 'yet', or 'even then') in the main clause when 'Although' is already present.

Sentence Analysis

Let's analyze each option:

• (a) Although it was raining, we had the picnic. This sentence correctly uses 'Although'. The contrast between the rain and having the picnic is established without redundancy. This is grammatically sound.
• (b) Although it was raining, still we had the picnic. The adverb 'still' creates redundancy because 'Although' already indicates the contrast.
• (c) Although it was raining, yet we had the picnic. The conjunction 'yet' is redundant here for the same reason as 'still'.
• (d) Although it was raining, even then we had the picnic. The phrase 'even then' also creates redundancy after 'Although'.

Therefore, the sentence that correctly follows standard grammatical rules is option (a).

Correct Sentence Identification

Based on the analysis, the correct sentence is:

Although it was raining, we had the picnic.