---3----
---3----
---0----
---0----
---x----
---3----

A. You are not missing the string, but muting it. The X in this chord means to mute the string indicated. Touch the string very lightly with the closest finger that you are already using in the chord. Strum all of the strings at the same time, but the 5th string will not sound because you are lightly touching it.

---3---- 4th finger
---3---- 3rd finger
---0---- open
---0---- open
---x---- mute with your 2nd finger
---3---- 2nd finger

Sometimes you see this.

---3----
---3----
---0----
---0----
--------
---3----

This can also be a little confusing. This does not mean you miss the 5th string either. You will play it the same way as above, just mute the 5th string. If you see what looks to be a chord, but there is a string with nothing on it, mute it.