Parts of a sentence are given below. While the first part is in the correct…

Concept: In a jumbled-sentence question, a single sentence is broken into unordered clauses/phrases that must be reassembled into one coherent sentence. The correct order is fixed by grammatical connectors (conjunctions such as 'but', correlative pairs such as 'so far ... but ... from now on') that signal contrast or sequence between specific clauses, and by semantic/logical adjacency, where a modifying or purpose phrase must sit next to the exact word or clause it modifies. A comma-marked adverbial unit (like 'from now on,') is built to sit immediately next to the conjunction that introduces the clause it opens — nothing may be wedged between them. Only one ordering satisfies every connector and adjacency constraint at once.

Application: Starting from the fixed opening 'I had been going', each part is placed by checking what it must connect to:

1. 'to school by car so far, but' (Q) attaches first: 'so far' pairs with the ongoing past action 'I had been going', and 'but' is the conjunction that will introduce the contrasting decision.

2. 'from now on, I will be going' (O) follows immediately, right after 'but': its internal comma marks it as the fronted time-adverbial for the NEW main clause, and 'from now on' is the direct correlative partner of 'so far' — nothing may separate this pair from the conjunction that joins them.

3. 'by the school van' (R) comes next: it is the means of transport for the NEW action, mirroring 'by car' attached to the old action.

4. 'to do my bit for the environment' (P) closes the sentence: a purpose clause explaining WHY the switch is being made belongs at the end, once the new action itself has been stated.

Contrast: none of the other orderings keep every connector and adjacency constraint resolved:

• QPOR wedges 'to do my bit for the environment' between 'but' and 'from now on,' — this breaks the matched 'so far ... but ... from now on' correlative pair that the comma inside 'from now on,' is built to complete, and forces 'from now on' to attach to the purpose infinitive instead of introducing the new main clause, producing a needlessly convoluted structure instead of the direct contrast the conjunction sets up.

• PQOR attaches 'to do my bit for the environment' right onto the opening 'I had been going', turning the past-habit clause into a garbled 'was going to do my bit ... to school by car' construction and burying the 'so far, but' contrast mid-sentence.

• RQPO puts 'by the school van' on the very first clause, so the sentence claims the OLD daily routine used the van — clashing with 'by car', which belongs there instead.

Hence the coherent sentence is: 'I had been going to school by car so far, but from now on, I will be going by the school van to do my bit for the environment' — order Q-O-R-P (QORP).