What is the function of the iris in the eye of a frog?

Which one of the following pairs of structures is correctly matched with their description?

Description	Structures
$a$. Tibia and fibula	Both form parts of knee joint
$b$. Cartilage and cornea	No blood supply but do require oxygen for respiratory need
$c$. Shoulder joint and elbow joint	Ball and socket type of joint
$d$. Premolars and molars	$20$ in all and $3$ rooted

Which of the following statements is correct?

Which teeth fall out in mammals?

How many organ systems are integrated for locomotion in humans?
Nervous system,Endocrine system,Muscular system,Skeletal system,Circulatory system

Analogy type questions:
$(1)$ During muscle contraction,the $A$-band does not change in length.
$(2)$ The $8^{th}$,$9^{th}$,and $10^{th}$ pairs of ribs are attached to the $7^{th}$ pair of ribs with the help of hyaline cartilage. Identify the terms.