Compare the knowledge of persons $X, Y, Z, A, B$ and $C$ in relation to each other.
$X$ knows more than $A$.
$Y$ knows as much as $B$.
$Z$ knows less than $C$.
$A$ knows more than $Y$.
The best knowledgeable person amongst all is:

There are six persons $A, B, C, D, E$ and $F$ in a school. Each of the teachers teaches two subjects,one compulsory subject and the other optional subject. $D's$ optional subject was History while three others have it as a compulsory subject. $E$ and $F$ have Physics as one of their subjects. $F's$ compulsory subject is Mathematics,which is an optional subject of both $C$ and $E$. History and English are $A's$ subjects,but in terms of compulsory and optional subjects,they are the reverse of those of $D$. Chemistry is an optional subject of only one of them. The only female teacher in the school has English as her compulsory subject. Disregarding which is the compulsory and which is the optional subject,who has the same two-subject combination as $F$?

$A, B, C, D, E, F,$ and $G$ are members of a family consisting of $4$ adults and $3$ children,two of whom,$F$ and $G$,are girls. $A$ and $D$ are brothers and $A$ is a doctor. $E$ is an engineer married to one of the brothers and has two children. $B$ is married to $D$ and $G$ is their child. Who is $C$?

In a group of six women,there are four dancers,four vocal musicians,one actress and three violinists. Girija and Vanaja are among the violinists while Jalaja and Shailaja do not know how to play the violin. Shailaja and Thanuja are among the dancers,Jalaja,Vanaja,Shailaja and Thanuja are all vocal musicians and two of them are also violinists. If Pooja is an actress,who among the following is both a dancer and a violinist?

Among five boys,Vineet is taller than Manick,but not as tall as Ravi. Jacob is taller than Dilip but shorter than Manick. Who is the tallest in their group?

$A, B, C, D, E$ and $F$,not necessarily in that order,are sitting on six chairs regularly placed around a round table. It is observed that:
$A$ is between $D$ and $F$.
$C$ is opposite to $D$.
$D$ and $E$ are not on neighbouring chairs.
Which one of the following pairs must be sitting on neighbouring chairs?