abstract : abstract;
as : type conversion;
base : access the members of the base class from the derived class;
checked : explicitly enable overflow checking for integer type arithmetic operations and conversions;
decimal : Represents a 128-bit data type, which has higher precision and a smaller range than floating-point types, suitable for financial and monetary calculations;
extern : Use the extern modifier in a method declaration to support implementing a method externally. A common way of extern modifiers is to be used with the DllImport attribute when using the Interop service to call into unmanaged code; in this case the method must also be declared static;[DllImport("avifil32.dll")]public static extern void Foo();public extern static void Fill();
interface : defines the interface;
internal : can only be accessed in this assembly;
lock : marks a block of statements as a critical section by acquiring a mutex lock on a given object, executing the statement, and releasing the lock;
operator : overloaded operator, user-defined conversion;
ref is in and out and must be initialized first;
out is only out but not in;
Override override is to override the method in the parent class in the subclass;
params to implement variable parameters;
readonly：