Read the article and select the best answer. Article: Humans have long been interested greatly in the idea of being able to walk on water. Sadly, biological facts prevent us ever realizing this dream without artificial aid--we simply weigh too much, and all our weight pushes down through our relatively small feet, resulting in a lot of pressure that makes us sink. However, several types of animals can walk on water. One of the most interesting is the common basilisk Basilicus basilicus, a lizard native to Central and South America. It can run across water for a distance of several meters, avoiding getting wet by rapidly hitting the water's surface with its feet. The lizard will reach a speed of 20 steps per second to keep moving forward. For humans, we would need huge feet that we could bring up to our ears in order to create enough "hitting". But fortunately there is an alternative: cornflour . By adding enough of this common thickening agent to water (and it does take a lot), you can create a special mixture that doesn't behave like normal water. Now, if the surface of the water is hit hard enough, particles in the water get together for a moment to make the surface hard. Move quickly enough and put enough force into each step, and you really can walk across the surface of this adequately thick liquid of cornflour. Fun though all this may sound, it's still rather messy and better read about in theory than carried out in practice. If you must do it, then keep the water wings ready in case you start to sink--and take a bath afterward! Question: Walking on water hasn't become a reality mainly because humans _ . Options: A: are not interested in it B: are afraid to make an attempt C: have not invented proper tools D: have biological limitations
D