Which of the following is a valid SQL statement?
a. CREATE TABLE tablel
    (col1 NUMBER PRIMARY KEY,
    col2 VARCHAR2 (20) PRIMARY KEY,
    col3 DATE DEFAULT SYSDATE,
      col4 VARCHAR2 (2));

b. CREATE TABLE tablel
    (col1 NUMBER PRIMARY KEY,
    col2 VARCHAR2(20),
    col3 DATE,
    col4 VARCHAR2 (2) NOT NULL,
    CONSTRAINT tablel_col3_ck
      CHECK (col3=SYSDATE));

c. CREATE TABLE tablel
   (col1 NUMBER,
   col2 VARCHAR2 (20),
   col3 DATE,
   col4 VARCHAR2 (2),
   PRIMARY KEY (coll));

d. CREATE TABLE tablel
    (coll NUMBER,
    col2 VARCHAR2 (20),
    col3 DATE DEFAULT SYSDATE,
    col4 VARCHAR2 (2);