Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE Student (StuID VARCHAR, age INTEGER); CREATE TABLE Participates_in (StuID VARCHAR, age INTEGER)
### Question:
Show the ids for all the students who participate in an activity and are under 20.
### Answer:
SELECT StuID FROM Participates_in INTERSECT SELECT StuID FROM Student WHERE age < 20