There legs had to adapt to their new surroundings in order to survive so as time passed they evolved. I think it’s called natural selection.
The correct choice is that it extends until depths of around 60 m where sediments cannot move anymore. The important thing is that it certainly is not just the contact point of water and land; it goes into the sea until this point, where also enough light reaches the bottom for plants to do photosynthesis. D is wrong because breakers do not play a role in this definition, although it can vary from context to context (sea, lakes etc.).
Enzyme may work if in it's optimum pH if the pH didn't match with the enzyme's pH, the enzyme will break down.
Enzyme will break down if the temperature so high it's called denaturation.
The correct answer here is "cell membrane". Generally it makes sure that nothing enters or leaves the cell, except by its highly guarded "gates", such as ion channels, that let some particles through - but they're very picky about whom to let in!
