A sentential form is the start symbol $S$ of a grammar or any string in $(V \cup T)^*$ that can be derived from $S$.
Consider the linear grammar
$(\{S, B\}, \{a, b\}, S, \{S \rightarrow aS, S \rightarrow B, B \rightarrow bB, B \rightarrow \lambda \})$.
A derivation using this grammar might look like this:
$S \Rightarrow aS \Rightarrow aB \Rightarrow abB \Rightarrow abbB \Rightarrow abb$
Each of $\{S, aS, aB, abB, abbB, abb\}$ is a sentential form.
Because this grammar is linear, each sentential form has at most one variable. Hence there is never any choice about which variable to expand next.
Here, in option D the sentential forms are same but generated differently coz we are using here Bottom Up production.
Handle:
for example the grammar is:
$$\begin{align*} E &\rightarrow E+n\\ E &\rightarrow E*n\\ E &\rightarrow n \end{align*}$$
Then say to derive string $n+n*n$:
these are three different handles shown in $3$ different colors = $\left\{ n, E+n, E*n \right \}$
that's what option D says