void setup() {
  Serial.begin(115200);
  pinMode(D2, OUTPUT);
  pinMode(D3, OUTPUT);
  pinMode(D4, OUTPUT);
  pinMode(D10, INPUT_PULLUP); //set as INPUT_PULLUP, which mean active the pullup resistor inside the microcontroller, avoiding the short circuit when the button is pressed.
  pinMode(D9, INPUT_PULLUP);  //when pin is set as pull up, the digital read result will always be 1
  pinMode(D8, INPUT_PULLUP);  //and only become 0 when the button is pressed.
}

void loop() {
  if (digitalRead(D10)==0){digitalWrite(D2, HIGH);} //
  else { digitalWrite(D2, LOW);}

  if (digitalRead(D9)==0){digitalWrite(D3, HIGH);}
  else { digitalWrite(D3, LOW);}

  if (digitalRead(D8)==0){digitalWrite(D4, HIGH);}
  else { digitalWrite(D4, LOW);}
}