Question

The classification system given by Linnaeus was based on
(a)Androecium structure
(b)Flower arrangement
(c)Leaf morphology
(d)Plant habit

Answer 1

Hint: It is the third arrangement of floral organs made out of stamens or microsporophylls. Ordinarily, each stamen consists of a slender stalk-like filament sup­porting a knob-like spore case or the anther. Each anther consists of two lobes (anther lobes) connected by a connective which may be clearly seen on the dorsal side as an extension of the filament.

Complete answer
Carolus Linnaeus is considered the 'Father of Taxonomy'. He developed how to call and organize species.
Linnaeus’s artificial system of classification was supported by the androecium structure. The significance of flower and fruit structures was first recognized by him. He emphasized the essential numerical characteristics of sexual parts i.e., stamens and carpels. Thus the Linnaeus system is also known as a sexual system.

Additional information
Every other lobe, once more, has two pollen sacs or pollen chambers set longitudinally. There are longitudinal grooves or sutures along the ventral face of the anther demarcating the pollen chambers. Every pollen chamber represents a microsporangium and contains incalculable microspores of pollen The stamen, therefore, may be a microsporophyll bearing four microsporangia. While this is often the traditional case, there are some flowers where the anther possesses only two pollen chambers (i.e., bisporangiate) and in Malvaceae even these two pollen chambers fuse developing a mature unilocular anther.
A flower may some­times be reduced to one stamen as seen within the cyathium inflorescence.

So the correct answer is ‘Androecium structure

Note: In early androecium development either distinct pentagonal androecial ring walls or five common petal/androecium primordia are present. Ring walls produce 5 ante petalous and five alternipetalous primary androecial primordia. Normal primordia partition into peripheral petal primordia and antepetalous essential androecial primordia.