Let us consider the following relational database.

Songs$($albumID$,$ artistID, songTitle, length$)$

The following SQL query is for retrieving the number of songs with a length of $160$ seconds for each artist.

SELECT artistID, COUNT$(*)$

FROM Songs

WHERE length $=\text{'}160$ sec$.\text{'}$;

Which section of the query is illegal?

a$.$ length in the WHERE clause.

b$.$ COUNT$(**)$ in the SELECT clause.

c$.$ artistID in the SELECT clause $.$

d$.$ The GROUP BY artistID clause should be added.