for this type of question we need to consider two numbers as examples.
Let us take one number as 3 and other odd number as 7 
Now multiplying both , we get , 7 x 3 = 21 which is again an odd number . 
Why is my answer always correct? 
Let us try with other set of examples too, 
Example 1 : 
Multiplying 5 and 9 
=> 5 x 9 = 45 is an odd number 
Multiplying 3 and 9
=> 3 x 9 = 27 is an odd number 
Hence whenever we multiply two odd numbers , we always get an odd number .