Let A$,$ B$,$ C denotes the set of students in CS$1300$ proficient in Java, C$++,$ and Python. The

total number of students in the class is $100$ and everyone is proficient in Java. There are $40,$

and $30$ students who are proficient in C$++,$ and Python respectively. The number of students

who are proficient in both C$++$ and Python is $10.$ How many students proficient only in Java

$?$

A$.20$ B$.30$ C$.40$ D$.50$