Since nobody gave him any help, he    have done the research on his own.

If human beings had been a bit less greedy and cruel, more birds and animals _____dying out.

You _____ return my dictionary now. You can keep it and I will get it from you later.

He ignored the neighbor's request that ________ less noise at night.

—What is an ideal team leader like?—He ______ be responsible, determined and creative．