function sendCollaterals(address _to, address[] memory _tokens, uint[] memory _amounts) external override returns (bool) {
    _requireCallerIsBOorTroveMorTMLorSP();
    require(_tokens.length == _amounts.length);
    for (uint i = 0; i < _tokens.length; i++) {
        _sendCollateral(_to, _tokens[i], _amounts[i]); // reverts if send fails
    }

    if (_needsUpdateCollateral(_to)) {
        ICollateralReceiver(_to).receiveCollateral(_tokens, _amounts);
    }
    
    return true;
}
function _sendCollateral(address _to, address _collateral, uint _amount) internal returns (bool) {
    uint index = whitelist.getIndex(_collateral);
    poolColl.amounts[index] = poolColl.amounts[index].sub(_amount);
    bool sent = IERC20(_collateral).transfer(_to, _amount);
    require(sent);

    emit ActivePoolBalanceUpdated(_collateral, _amount);
    emit CollateralSent(_collateral, _to, _amount);
}
poolColl.amounts[index] = poolColl.amounts[index].sub(_amount);
