Road running often offers those 19 a range of challenges such as dealing with hills, sharp bends, rough weather, and so on.
答案：(B) involved
those involved 是固定用法，意為「參與其中的人」，involved 是過去分詞當形容詞、帶被動語意；involving 為主動，to involve 是不定詞，are involved 會使句子出現兩個動詞。
involve 你大概只記得「牽涉」，而且多半見於 be involved in an accident（捲入事故），所以看到 those ___ 這個位置不知道要填什麼。those involved 就是「參與其中的人」，等於 those who are involved，是英文很常用的簡潔說法。
這一格填的不是動詞，是說明 those 是哪些人的字。Road running often [offers] [those ___] [a range of challenges] such as dealing with hills. offers 已經是主要動詞，後面兩個方括號是它的兩個受詞，人在前、物在後，這是 offer sb sth 的形狀；空格落在第一個受詞裡面。完整說法是 those who are involved（參與其中的人），把 who are 省掉，就剩下名詞後面直接接分詞。這是形容詞子句的簡化，判斷方式只有一句：名詞在做那個動作用 V-ing，被那個動作影響用 p.p.。人是被牽涉進來的一方，所以用 involved。同一組一起記：the people concerned（相關人士）、the items mentioned（提到的那幾項）、the students selected（獲選的學生）。順帶一提，involved 也可以是過去式動詞，所以有人會把 those involved a range of challenges 讀成一個完整句子（那些人牽涉了一連串挑戰）。但這樣切，offers 就沒有受詞了，切不通。
involving 是現在分詞，方向相反——人是被牽涉的一方，不是去牽涉別人。to involve 放在名詞後面表示「將要做的、有待做的」（the work to do 待辦的工作），與後面的挑戰接不上。are involved 是有時態的動詞，而有時態的動詞不能直接掛在名詞後面當修飾語，要用它就得補回關係代名詞，寫成 those who are involved。
those involved（參與其中的人）、the people concerned（相關人士）、be involved in（涉入、參與）、get involved（參與其中）、offer sb sth（提供某人某物）、involvement（參與）。
Road running is one of the most popular and accessible athletic activities in the world. It refers to the sport of running on paved roads or established paths as opposed to track and field, or cross country running. The three most common 16 for road running events are 10K runs, half marathons (21.1K), and marathons (42.2K).
Road running is unique among athletic events because it 17 all ages and abilities. In many cases first time amateurs are welcome to participate in the same event as running club members and even current world-class 18 . Sometimes it may also include wheelchair entrants.
Road running often offers those 19 a range of challenges such as dealing with hills, sharp bends, rough weather, and so on. Runners are advised to train prior to participating in a race. Another important factor contributing to success is a suitable pair of running shoes.
Road running is often a community-wide event that highlights or raises money for an issue or project. 20 , Race for the Cure is held throughout the U.S. to raise breast cancer awareness. This race is also run in Germany, Italy, and Puerto Rico.