1.
a. Look, I (have) have two tickets for the circus.
b. Look, I (hold) am holding two tickets for the circus.

2.
a. We (be) had been there for more than half an hour by the time the show began.
b. We (wait) had been waiting there for more than half an hour by the time the show began.

3.
a. Sam (sit) was sitting in the seat next to me when the clown threw a bucket of water at me.
b. Sam (be) was in the seat next to me when the clown threw a bucket of water at me.

4.
a. One clown was juggling while he (balance) was balancing a glass of wine on his head.
b. One clown was juggling while he (have) had a glass of wine on his head.

5.
a. I (love) have loved the circus ever since I was a child.
b. I (go) have been going to the circus ever since I was a child.

6.
a. Right now, I (see) see two elephants doing tricks in the ring.
b. Right now, I (look) am looking at two elephants doing tricks in the ring.