Which structure is statically determinate and stable with the loadings shown? Note: roll supports can only push. (a) (d) (b) (e) (c) (f) (a), (c), (d), (e), (f) (a), (b), (c), (d), (e) (a), (c), (e) (a), (b), (c), (d) (a), (c), (d), (e)