try to diagram the argument, numbering each of the sentences and using the 'THEREFORE TEST' (try 'x, therefore y' and 'y, therefore x', and see which, if either, of them makes sense).
1 Plant scientists have used genetic engineering on seeds to produce crop plants that are highly resistant to insect damage.
2 Unfortunately, the seeds themselves are quite expensive, and the plants require more fertilizer and water to grow well than normal ones.
3 Thus, for most farmers the savings on pesticides
...
1 Plant scientists have used genetic engineering on seeds to produce crop plants that are highly resistant to insect damage.
2 Unfortunately, the seeds themselves are quite expensive, and the plants require more fertilizer and water to grow well than normal ones.
3 Thus, for most farmers the savings on pesticides
...
