Although genetically engineered crop plants carrying traits like disease/herbicide/pest resistance would be very advantageous, they may yet pose a serious threat to the environment due to __________________.

The correct option is D Unpredictability of the consequences of introducing a gene in a new host

Solution : Genetically engineered crop plants are advantageous because of their high productivity or disease resistance but the consequences of introducing a new gene in the host is sometimes unpredictable and can cause problems higher up the trophic level.

So the correct answer is " Unpredictability of the consequences of introducing a gene in a new host."