I can't figure out why the correct anwer is a)

Each of 35 students learns at least one of these languages: English, German, French.

5 students study all of these languages.

20 students study English.

15 students study German

10 students study French.

Decide which of these statement is true:

a) No student exists, who learns exactly 2 languages.

b) At least one student learns exactly 2 languages.

c) At least one student learns French and German and doesn't learn English.

d) Described situation cannot happen.

d) None of the statements is correct.

I would greatly appreciate if you describe how you got the result.

Thank you.