Among the crises that face humans ________ the lack of natural resources．

A．is

B．are

C．is there

D．are there

An ecosystem consists of the living and nonliving things in an area ________ interact with one another．

A．that

B．where

C．who

D．what

________ at the photos, illustrations, title and headings and you can guess what the reading is about．

A．To look

B．Looking

C．Having looked

D．Look

I cannot hear the professor clearly as there is too much noise ________ I am sitting．

A．before

B．until

C．unless

D．where

Sophia got an e-mail ________ her credit card account number．

A．asking for

B．ask for

C．asked for

D．having asked for

Young people may risk ________ deaf if they are exposed to very loud music every day．

A．to go

B．to have gone

C．going

D．having gone

I have no idea ________ the cell phone isn't working, so could you fix it for me?

A．what

B．why

C．if

D．which

The students are looking forward to having an opportunity ________ society for real-life experience．

A．explore

B．to explore

C．exploring

D．explored

The judges gave no hint of what they thought, so I left the room really ________．

A．to be worried

B．to worry

C．having worried

D．worried

They promised to develop a software package by the end of this year, ________ they might have．

A．however difficult

B．how difficult

C．whatever difficulty

D．what difficulty