Aircrafts

Today, My teacher told me about the different general aircrafts and supersonic aircrafts. He said : “aircrafts have little chance to fly at 1 Ma for a long time.” This is because when an aircraft is flying at 1 Ma,
it bears the biggest drag force during the whole trip, and the wings of the aircraft are very easily to be fractured.
Many aircrafts usually fly at much more than 1 Ma or much less than 1 Ma. Supersonic aircrafts are the aircrafts that fly at more than 1 Ma. They are required to exceed the sonic in a very short time [Not sure what you mean here, maybe "exceed the speed of sound?"].
Besides, he asked me that which is better: fluid fuel and  or solid fuel better. I knew most Chinese missiles use solid fuels. Solid fuel does not need to be filled, which is safe and time-saving. However, it has a big disadvantage. It has friction with the wall of the rocket which produces high temperatures and makes the rocket body shake. And Although fluid fuel need to be filled for a long time takes longer to fill (one and a half days in general) and is more dangerous, it can provide rocket and large missiles with more energy. I thought solid fuel and fluid fuel have their own advantages and disadvantages. Which one is better depends on the situations. I like my teacher, because he always tell me something that interests me. I sincerely hope that I have a chance to engage in the work about national defense and weapons in the Chinese academy of science in the future like him! In order to achieve the goal, I will study hard.