单选题 选出应填入下面一段英语中______内的正确答案。
   Prior to the UML, there was no clear leading (1) language. Users had to choose. from among many similar modeling languages with minor differences in overall (2) power. Most of the modeling languages shared a set of commonly accepted concepts that are expressed slightly differently in various languages. This lack of (3) discouraged new users from entering the OO market and from doing OO modeling, without greatly expanding the power of modeling. Users longed for the industry to it adopt one, or a very few, broadly supported modeling languages suitable for (4) usage.
   Some vendors were discouraged from entering the OO modeling area because of the need to support many similar, but slightly different, modeling languages. In particular, the supply of add-on tools has been depressed because small vendors cannot afford to support many different formats from many different (5) modeling tools. It is important to the entire OO industry to encourage broadly based tools and vendors, as well as niche products that cater to the needs of specialized groups.