Task: Question Answering
Input (English): Passage: The underground punk rock movement inspired countless bands that either evolved from a punk rock sound or brought its outsider spirit to very different kinds of music. The original punk explosion also had a long-term effect on the music industry, spurring the growth of the independent sector. During the early 1980s, British bands like New Order and the Cure that straddled the lines of post-punk and new wave developed both new musical styles and a distinctive industrial niche. Though commercially successful over an extended period, they maintained an underground-style, subcultural identity. In the United States, bands such as Hüsker Dü and their Minneapolis protégés the Replacements bridged the gap between punk rock genres like hardcore and the more melodic, explorative realm of what was then called "college rock".A 1985 Rolling Stone feature on the Minneapolis scene and innovative California hardcore acts such as Black Flag and Minutemen declared, "Primal punk is passé. The best of the American punk rockers have moved on. They have learned how to play their instruments. They have discovered melody, guitar solos and lyrics that are more than shouted political slogans. Some of them have even discovered the Grateful Dead." By the mid-to-late 1980s, these bands, who had largely eclipsed their punk rock and post-punk forebears in popularity, were classified broadly as alternative rock. Alternative rock encompasses a diverse set of styles—including indie rock, gothic rock, dream pop, shoegaze, and grunge, among others—unified by their debt to punk rock and their origins outside of the musical mainstream.As American alternative bands like Sonic Youth, which had grown out of the no wave scene, and Boston's Pixies started to gain larger audiences, major labels sought to capitalize on the underground market that had been sustained by hardcore punk for years. In 1991, Nirvana emerged from Washington State's underground, DIY grunge scene; after recording their first album, Bleach for about $600, the band achieved huge (and unexpected) commercial success with its second album, Nevermind. The band's members cited punk rock as a key influence on their style. "Punk is musical freedom", wrote frontman Kurt Cobain. "It's saying, doing, and playing what you want." Nirvana's success opened the door to mainstream popularity for a wide range of other "left-of-the-dial" acts, such as Pearl Jam and Red Hot Chili Peppers, and fueled the alternative rock boom of the early and mid-1990s. 
Question: What two punk rock genres did the Replacements and Hüsker Dü build the gap between?
Output (English): hardcore.