Plant reproduction often requires pollen, and hay fever or pollen allergy is the most prevalent allergy. Given these facts, what is required for plant reproduction among the following options:
- By wind and rain
 - Something that is found on a cloud
 - fertilization occurs
 - Males and females
 - Something that comes from a volcano
 - Something that is invisible
 - Something that causes allergies
 - sperm and egg fuse


 

       Something that causes allergies  