两个都可以的,口语中都用得到,而且老师也是这样教的
“in formal English the comparative degree is " more friendly" (Pat is more friendly than her sister). In informal English "friendlier than" is pretty much used (Pat is friendlier than her sister).
The superlative degree is "the most friendly of" (Pat is the most friendly of all my cousins / [...[ the friendliest of them all).”
