Here im posting Trigger and Testclass. Plz help in code coverage....Urgent......

Trigger:

trigger Update_completed_activities_in_Opportunity on Task (after update)
{
list<opportunity> liOpportunities = new list<opportunity>();
list<id> liIDs = new list<id>();

for(Task sTask : trigger.new)
{
if(sTask.Status == 'Completed' && ('' + sTask.WhatId).startsWith('006'))
{
liIDs.add(sTask.WhatId);
}
system.debug('Task123'+sTask);
for(Opportunity sOppty : [ select id,Welcome_Call_Completed__c, 
Welcome_Kit_Dispatched__c,
Agreement_Amount_Received__c,
Construction_Agreement_Received__c,
Sale_Agreement_Received__c from Opportunity where Id in : liIDS])

{
system.debug('sOppty123'+sOppty); 
if (liOpportunities .isEmpty())
{
return; // the task is not referring to an opportunity so exit the trigger
}
sOppty = liOpportunities[0]; // the zero'th, i.e. first (only) opportunity in the lis


liOpportunities.add(sOppty);
system.debug('OpportunityList'+liOpportunities);

if(sTask.Status == 'completed' && sTask.Subject == 'Welcome Call' && !sOppty.Welcome_Call_Completed__c)
{
sOppty.Welcome_Call_Completed__c = true;
}
if(sTask.Status == 'completed' && sTask.Subject == 'Dispatch Welcome Kit' && !sOppty.Welcome_Kit_Dispatched__c)
{
sOppty.Welcome_Kit_Dispatched__c = true;
}
if(sTask.Status == 'completed' && sTask.Subject == 'Collect Agreement Amount' && sOppty.Agreement_Amount_Received__c == Null)
{
sOppty.Agreement_Amount_Received__c = System.today();
}
if(sTask.Status == 'completed' && sTask.Subject == 'To check physical receipt of Agreement Copies' && !sOppty.Construction_Agreement_Received__c && !sOppty.Sale_Agreement_Received__c)
{
sOppty.Construction_Agreement_Received__c = true;
sOppty.Sale_Agreement_Received__c = true;
}
}
}
update liOpportunities;
}

 TestClass:

@isTest
private class Activity_Receipt_Trigger_Test{


    static testMethod void myopptyTest() {
     
     
        Account A = new account(name='Ac');
        insert A;
        
        Opportunity O = new opportunity (name='Oppty', 
                                         Accountid = A.id, 
                                         Stagename = 'Sold', 
                                         CloseDate = System.Today(),
                                         Welcome_Call_Completed__c = False,
                                         Welcome_Kit_Dispatched__c = False,
                                         Agreement_Amount_Received__c = Null,
                                         Construction_Agreement_Received__c = False,
                                         Sale_Agreement_Received__c = False);
        insert O;
        
        Task T = new task(Subject='Welcome Call', Status='Not Started', whatid = O.id);
        insert T;
        Task T1=new task(Subject='Dispatch Welcome Kit', Status='Not Started', whatid = O.id);
        insert T1;
        Task T2=new task(Subject='Collect Agreement Amount' , Status='Not Started', whatid = O.id);
        insert T2;
        Task T3=new task(Subject='To check physical receipt of Agreement Copies' , Status='Not Started', whatid = O.id);
        insert T3;
        Receipt__c R = new Receipt__c (name='test123', Realization_status__c = 'Not Done', Payment_Towards__c = 'Agreement Signing', Opportunity__c = O.id);
        insert R;
        R.Realization_Status__c ='Done';
        Update R;
       
        T.Status = 'Completed';
        T1.Status='Completed';
        T2.Status='Completed';
        T3.Status='Completed';
        Update T;
        Update T1;
        Update T2;
        Update T3;
        O.Agreement_Amount_Realized__c = System.today();
        O.Agreement_Amount_Received__c = System.today();
        O.Booking_Amount_Realized__c = System.today();
        O.Welcome_Call_Completed__c = true;
        O.Welcome_Kit_Dispatched__c = true;
        O.Construction_Agreement_Received__c = true;
        O.Sale_Agreement_Received__c = true;
        
        Update O;
        
}
}