现在进行时（be + v-ing） — 英语填空题

Read and complete: It is Sunday morning. Tom is in the zoo. Listen! The birds ___ (sing) in the trees. Look! An elephant ___ (drink) water by the river. Two tigers ___ (run) fast, but a baby tiger ___ (sleep) under the tree. What ___ the pandas doing? They ___ (eat) leaves.