From left, a lens labeled 1 flat on the left and convex on the right, a thick lens labeled 2 double convex, a lens labeled 3 convex on the right and slightly concave on the left, a lens labeled 4 flat on the left and concave on the right, a lens labeled 5 concave on both left and right, a thin lens labeled 6 double convex.
Which lenses are convex? Check all that apply.

1
2
3
4
5
6