Mastering Blockchain Programming with Solidity

The MSTCrowdsale.sol contract

According to our contract design and architecture, we will create the MSTCrowdsale.sol contract.  The following is the code for the MSTCrowdsale.sol contract:

pragma solidity >=0.5.0 <0.6.0;import "openzeppelin-solidity/contracts/crowdsale/validation/TimedCrowdsale.sol";import "openzeppelin-solidity/contracts/crowdsale/emission/MintedCrowdsale.sol";import "openzeppelin-solidity/contracts/crowdsale/validation/CappedCrowdsale.sol";import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";contract MSTCrowdsale is    CappedCrowdsale, TimedCrowdsale, MintedCrowdsale {    constructor(        uint256 _rate,        address payable _wallet,        IERC20 _token,        uint256 _openingTime,        uint256 _closingTime,        uint256 _cap    ) Crowdsale(_rate, _wallet, ...