Approximately how many cells are found in the body of an adult human?

Which of the following is a correctly matched pair?

The cell is a wonder of the world because ...........

Who proposed the modern cell theory?

Match column-$I$ (scientists) with column-$II$ (discovery) and select the correct option.

Column-$I$	Column-$II$
$A$. Leeuwenhoek	$I$. First saw and described a living cell
$B$. Robert Brown	$II$. Presence of cell wall is unique to plant cells
$C$. Schleiden	$III$. Discovered the nucleus
$D$. Schwann	$IV$. All plants are composed of different kind of cells

Assertion: Organisms are made up of cells.
Reason: Cells are the structural unit of living organisms. $A$ cell keeps its chemical composition steady within its boundary.