Place the fern structures in the correct order to fill in the blanks in the following statement:
In Leptosporangiate ferns, __(1)__ are small structures with a wall that is a single cell-layer thick. They have a band of thickened cells called a(n) __(2)__, which changes shape with changes in humidity to throw __(3)__ into the air for dispersal. These structures are usually aggregated in clusters called __(4)__ on the bottoms of fertile leaves, and these clusters are each protected by a flap of tissue known as a(n) __(5)__.
a. sporangia; annulus; spores; sori; indusium
b. sori; indusium; spores; annulus; sporangia
c. spores; sporangia; sori; indusium; annulus
d. sori; indusium; spores; sporangia; annulus
e. sporangia; annulus; sori; indusium; spores