1. Robert writes... (present simple)
2. Robert wrote... (past simple)
3. Robert will write... (future simple)
1. Robert is writing... (present continuous)
2. Robert was writing...(past continuous)
3. Robert will be writing...(future continuous)
1. Robert has written... (present perfect)
2. Robert had written...(past perfect)
3. Robert will have written...(future perfect)
1. Robert has been writing... (present perfect continuous)
2. Robert had been writing...(past perfect continuous)
3. Robert will have been writing...(future perfect continuous)