Which one of these is the title of a UK number-one single by So Solid Crew?

"21 Seconds" is a song by UK garage crew So Solid Crew. It was released as the second single from the debut album "They Don't Know", and was the first of five consecutive top-20 hit singles for the group. It topped the UK Singles Chart in August 2001 and peaked just outside the top 40 in the Netherlands. It achieved first week sales of 118,135 units in the United Kingdom.

The song title alludes to the approximate 21 seconds that each of the band members is given to perform their rap. 21 seconds is arrived at as the song's tempo is approximately 140BPM and each rapper has 12 bars of 4 beats (48 beats at 140BPM, when worked out to the nearest integer, rounds to 21 seconds).

So Solid Crew are a British UK garage and hip hop collective originating from the area on and surrounding the Winstanley and York Road Estates in Battersea, London which achieved wide success in the early 2000s. The group consisted of many members, the most notable being Asher D (Ashley Waters), Lisa Maffia, Harvey and Romeo.

So Solid have been credited for being pioneers in the UK music scene. By turning UK garage from a dancey-genre to one that was darker and more MC-oriented, and gaining mainstream success, they inspired London youth to experiment with their own darker sounds, leading to what would become known as grime music.