Consider the following statements:

An in-line four-cylinder four-stroke engine is completely balanced for 1). primary forces 2). secondary forces 3). primary couples 4). secondary couples Of these statements

(a) 1,3 , and 4 are correct

(b) 1,2, and 4 are correct

(c) 1 and 3 are correct

(d) 2 and 4 are correct.