In rural road construction, the use of which of the following is preferred for ensuring environmental sustainability or to reduce carbon footprint? 1. Copper slag 2. Cold mix asphalt technology 3. Geotextiles 4. Hot mix asphalt technology 5. Portland cement. Select the correct answer using the code given below:

1. Copper slag — An industrial by-product that can be used in road construction in place of natural aggregates/fillers, helping waste utilization and lowering resource extraction. Verdict: Correct.

2. Cold mix asphalt technology — Preferred in rural roads because it avoids heating aggregates/bitumen, thus saving fuel and reducing emissions. Verdict: Correct.

3. Geotextiles — Improve subgrade strength, drainage and pavement life, reducing material use and maintenance burden. Verdict: Correct.

4. Hot mix asphalt technology — Requires heating and higher energy input, so it has a larger carbon footprint than cold mix. Verdict: Incorrect.

5. Portland cement — Conventional cement is carbon-intensive in production; it is not preferred on sustainability/carbon-footprint grounds here. Verdict: Incorrect.

Hence, 1, 2 and 3 only are preferred.