Detailed Explanation:

Answer: Option 2 — To detect gravitational waves

The evolved Laser Interferometer Space Antenna (eLISA), now known as LISA (Laser Interferometer Space Antenna), is a space-based gravitational wave observatory designed to detect low-frequency gravitational waves from cosmic sources. It uses laser interferometry to measure tiny distortions in spacetime caused by passing gravitational waves from events such as merging supermassive black holes, extreme mass ratio inspirals, and galactic binary systems. This ESA-led mission (with NASA contribution) operates in the millihertz frequency range, complementing ground-based detectors like LIGO that observe higher frequencies. The detection of gravitational waves opens a new window to observe the universe and test Einstein's general relativity in extreme conditions.