A. which B. what C. why D. that
A. on B. about C. with D. to
A. explain B. explaining C. to explain D. explained
A. experience B. experienced C. experiencing D. has experience
A. wide B. widen C. widely D. unwide
A. fast B. faster C. fastest D. fasten
A. pollute B. polluted C. pollution D. polluting
A. expect B. expected C. is expected D. is expecting