Answer:
Option 1, They only reproduce by self-pollination.
Step-by-step explanation:
There exists a pollinator isolation between the given two species of plants. Mimulus lewisii is pollinated by bees while Mimulus cardinalis is pollinated by humming bird. The two plant species pollinate with in their own species and thus there is no scope for cross pollination. Due to this difference, there in no possibility of natural interaction between Mimulus lewisii and Mimulus cardinalis and hence they breed separately.
Option 1 is correct