The correct choice is (a) when there is small spacing between the two sections placed back-to-back, washers and packing should be provided
The explanation: There should be minimum of two additional connection in between, spaced equidistant along the length of member. When there is small spacing between the two sections placed back-to-back, washers(in case of bolts) and packing(in case of welding) should be provided to make connection. When leg of angles greater than 125mm wide or web of channel is mm wide, minimum two bolts/rivets should be for connection.