1. skin tissue is more resistant to toxic substances than lung tissue and uses
2. skin tissue is more resistant to toxic substances than is lung tissue and uses
or
3. skin tissue is more resistant to toxic substances than lung tissue is and uses...
Without the 'is', No. 1 could imply that skin tissue is less resistant to lung tissue, which does not make sense.
not a teacher



Scientists have found that skin tissue is more resistant to toxic substances than lung tissue and uses sweat glands to protect the immune system from possible invaders.
skin tissue is more resistant to toxic substances than lung tissue and uses

